what are the main components of a TCR?
1 antigen binding site • variable regions • constant regions • transmembrane region • α chain • β chain
what is the difference between a BCR and a TCR's CD molecules?
on a B cell IgM and IgD are associated with CD79 • TCR is associated with CD3
what are the 2 classes of TCR?
α:β • γ:δ
how are gene rearrangements in a TCR similar to gene rearrangements in a BCR?
VDJ segments for beta and gamma chains • VJ segments for alpha and delta chains
unlike a B cell where a B cell carries IgM and IgD as antigen receptors, a T cell carries what?
either alpha beta receptor or gamma-delta receptor
which has more variation, V region of alpha and beta chain or V region of gamma and delta chains
V region of alpha and beta chains
generation of the variable region of TCR is generated the same way like in BCR, except what?
that TCR does not undergo somatic mutation
which enzymes are involved in TCR development?
RAG1 and RAG2 • the same enzymes involved in TCR development
generation of antigen-binding diversity for TCR depends on what?
the same somatic recombination and junctional mechanisms used for BCR diversity
How is diversity created in TCR?
1. joining of VDJ segments for beta and gamma chains • 2. joining of VJ segments for alpha and delta chains • 3. RAG-1 and RAG-2 encoded recombinase and TdT are required for somatic recombination • 4. junctional diversity
is there somatic hypermutation in TCR?
T cell progenitors originate from and develop where?
they originate from bone marrow and develop in the thymus
to what is the TCR's source of diversity in antigen recognition similar?
BCR because of random rearrangements of gene fragments VDJ and VJ
what is the structure of TCR?
has 2 peptides • α and β
how many epitope receptors does a TCR have?
how many CD3's is each TCR associated with?
what is the function of ζ peptides in TCR?
what are the co-receptor molecules of CDR's?
CD4 • CD8
when is Pre-TCR found?
on immature T cells; expressed early in development
when is TCR found?
on mature T cells
what is the major difference between pre-TCR and TCR?
pre-TCR has an incomplete α peptide: • pTα
how do T cell receptors recognize processed epitope?
in association with MHC
TCR require which co-receptors?
CD4 • CD8
which T cell type has co-receptor CD4?
Helper T cell
which T-cell type has the co-receptor CD8?
cytotoxic T cell
what is the MHC restriction of Helper T cells?
what is the MHC restriction of cytotoxic T cells?
what is the function of helper T cells?
B cells help macrophage activation • help for CD8 T cell cytokine secretion
what is the function of cytotoxic T cells?
killing virus infected cells • killing tumor cells
what are the parts of a CD4 co-receptor?
D1 • D2 • D3 • D4
what are the parts of the CD8 co-receptor?
α • β
what is the immune consequence of DiGeorge Syndrome?
What CD is expressed on a lymphoid precursor that just entered the thymus?
in the subcapsular zone of the thymus the cell becomes committed to develop to T cells by expressing what?
what are the two lines of development of committed CD2+ cells in the subcapsular zone?
beta-alpha expressing TCR • gamma-delta expressing TCR
in the beta-alpha line of development, the genes for beta gene segments are rearranged first and if it is productive, what happens next?
it is transcribe and translated to a beta chain that gets associated with a pTα.
what does a preT cell of the beta-alpha line express?
β • PTα
what happens if the pre T cell expressing β and PTα is functional?
the cell is signaled to rearrange the gene segments for α chain.
what is expressed on double positive T cells and where are they found?
double positive CD4+, CD8+ express TCR (βα) and are found in the cortex
What is positive selection in T cell development of the αβ line?
the TCR is checked if it can interact with MHC alleles of the person. • thymic epithelial cells present self antigen on MHC to the TCR. T cells expressing TCR that can interact with the MHC of the individual survive, if not they die
what is MHC restriction also known as?
where and by what cells is negative selection in T cell development carried out?
by dendritic cells in the corticomedullary junction
what happens in negative selection during T cell development?
dendritic cells present self antigens on MHC I and II to the double positive cells. T cells with high affinity die, T cell with weak or intermediate affinity live. T cells that survive either become CD4 or CD8 depending on their affinity to either MHC I or MHC II
what happens in terms of CD during T cell development, to T cells with affinity to MHC I molecules?
CD8 marker retained • CD4 will be lost
what happens in terms of CD during T cell development to T cells with affinity to MHC II molecules?
CD4 will be retained • CD8 will be lost
what are single positive T cells?
CD4+ or CD8+ and self tolerant
which type of T cells leave the thymus after T cell development?
what is AIRE?
autoimmune regulator gene that plays a role in negative selection to T lymphocytes specific to self antigens not found in the thymus
what is the purpose for AIRE's existence?
not all self antigens are present in the thymus to cause deletion of self reacting lymphocytes • -AIRE gene induces the expression of such self antigens in the thymus-m so that they can be used in negative selection
what % of the T cell pool is CD4-, CD8-, γδ+?
2-10% of total T cell pool
where are CD4-, CD8-, γδ+ cells found?
in tissue just before the dermis
do CD4-, CD8-, γδ+ T cells undergo selection?
how do CD4-, CD8-, γδ+ T cells emigrate?
Emigrate as CD4CD8 to epithelial tissues in skin, intestines and lungs
what is the function of CD4-, CD8-, γδ+ T cells ?
immunosurveillance of transformed, damaged, or stressed epithelial cells
what do CD4-, CD8-, γδ+ T cells recognize?
non-peptides • lipids • not completely identified (microbes or stressed host cells
do CD4-, CD8-, γδ+ T cells require APC?
what is the level of diversity of CD4-, CD8-, γδ+ T cells ?
what do naive T CD4 cells do upon exposure to antigens presented by APC?
differentiate into effector T CD4 cells
what are the effector T CD4 cells?
Th1 • Th2 • Th17 • Treg
the development of effector T CD4 cells depends on what?
cytokines in the environment, produced by the APC
what happens in naive T CD4 cells when they are exposed to the cytokines in the surroundings?
different transcription factors are activated
what do the effector T CD4 cells do?
produce a variety of cytokines that mediate different immunological activities
does clonal selection theory apply to T cell post antigen exposure development?
What happens in development of Th1?
naive T CD4, under the influence of IL-12 and IFN-γ, induces T-bet, producing Th1
what are the cytokines produced by Th1?
IL-2 • IFNγ
what is the major effector function of Th1?
Cell mediated immunity, • intracellular pathogens • Activate macrophages • Activate B cells and CD8
what happens in development of The2?
Naive T CD4, under the influence of IL-4, induces GATA-3, producing Th2
what are the cytokines produced by Th2?
IL-4 • IL-5 • IL-13 • IL-10
what are the major effector functions of Th2?
Humoral immunity, • B cell activation • extracellular pathogens • parasites and allergy
what happens in the development of Th17?
Naive T CD4, under the influence of IL-23, IL-6, IL-1 induces RORyt, producing Th17
what cytokines are produced by Th17?
Proinflammatory: • inflamamtion • autoimmunity • response to fungi and extracellular bacteria
what happens in the development of Treg?
Naive T CD4, under the influence of TGF-β, induces FoxP3, producing Treg
what cytokines are produced by Treg?
what are the major effector functions of Treg?
Down regulation: • Suppress other T cell subsets- anti-inflammatory activity
cytokines produced by Th1 act on what?
macrophages • NK cells • CD8 cells • B cells to switch to IgG1
cytokines produced by Th2 act on what?
eosinophils • B cells to switch to other class of IgG and IgE
cytokines produced by Th17 act on what?
neutrophils and epithelial cells
Treg acts on what cells?
other lymphocytes to prevent T cell proliferation
how many peptides in BCR?
how many peptides in TCR?
how many antigen binding regions in BCR?
how many antigen binding regions in TCR?
do TCR or BCR have variable and constant regions?
both have both
do TCR or BCR have gene segments and gene rearrangement?
both have both
what is the signal transducer molecule on BCR?
what is the signal transducer molecule on TCR?
Can BCR recognize free unprocessed antigen without MHC?
can TCR recognize free unprocessed antigen without MHC?
how does TCR recognize antigen?
recognize processed antigen in association with MHC on antigen presenting cells
what are the co-receptor molecules on TCR?
CD4 or CD8
from where does Tcell progenitor cell originate?
once a T cell progenitor migrates to the thymus, what can it develop into?
1. γδ (CD4-, CD8-); • 2. αβ cells (CD4+ or CD8+) carrying TCR
how does the source of antigenic diversity of TCR relate to BCR?
source of antigenic diversity of TCR is similar to BCR
what is the difference between αβ and γδ T cell development?
α:β T lymphocytes undergo through positive and negative selection in the thymus while γδ cells do not
AIRE gene has a role in what type of disease?
CD3 and zeta associated with TCR serves as what?
CD4 and CD8 are coreceptors of what?
TCR recognizes epitopes associated with what?
Which CD interacts with which MHC in TCR?
CD4 interacts with MHC II and CD8 interacts with MHCI
under the influence of cytokines in the environment, naive CD4 (helper cells differentiate into what?
into Th1 • Th2 • Th17 • Treg
what is the function of Th1, Th2, Th17, and Treg?
these subsets of cells produce different set of cytokines with different roles in the immune system
what are the pre-antigen exposure B cell stages?
Pro B cell--> • Pre B cell --> • Immature B cell--> • mature B cell
what are the post antigen exposure B cell stages?
mature B cells become either Plasma cells or Memory cells
pre antigen b cell development involves what?
generation of antigen specific receptors which are immunoglobulin molecules of IgM and IgD isotypes
what is the specificity of BCR?
is antigen (epitope) specific
what type of immunoglobulin is BCR?
membrane immunoglobulin (mIg)
BCR is associated with which CD?
what is the function of CD79 (Igα,β)?
it's a signal transducer
BCR belong to which two isotypes?
IgM • IgD
what is the similarity of the IgM and IgD on a single B cell clone?
both belong to the same idiotype (specific to a particular antigen)
the maturation stages of the B cell can be identified by what?
1. changes in enzyme activity • 2. CD marker expression • 3. synthesis of BCR (IgM and IgD)
CD10, CD19, and CD20 are markers of what?
is CD 20 found on plasma cells?
what cells is CD 20 found on?
early to late B cell • lymphoma cells
how many B cell clones and repertoires can a person generate?
in any given individual it is possible to generate 10^9-10^10 different B cell clones, each with different epitope binding regions
construction of a unique variable region is possible by the process known as what?
what factors contribute to somatic recombination?
1. existence of multiple copies of gene segments that code for the variable regions • 2. combinatorial diversity generated by random selection and combination of gene segments • 3. junctional diversity generated by addition of deletion of bases • 4. random assortment of light and heavy chains
on which chromosome is the λ light chain locus?
on which chromosome is the κ light chain locus?
on which chromosome is the heavy chain locus?
immunoglobulins are encoded by how many gene complexes?
3 gene complexes located on separate chromosomes
what are the functions of the 3 gene complexes located on separate chromosomes?
one for all heavy chains • one for κ chains • one for λ chains
how continuous are the gene complexes that code for immunoglobulins?
these genes are discontinuous and require translocations to be activated
what are the segments that encode the variable region of the light chain?
V • J
what are the segments that encode the variable region of the heavy chain?
V • D • J
what post-transcriptional processing do the gene complexes that encode immunoglobulin chains require?
DNA rearrangement • RNA splicing
what is the term for the process of gene rearrangement that occurs in generating BCR?
Cut and Paste process
RAG1 and RAG2 are what and what do they code for?
Recombination activating genes code for RAG1 and RAG2
what is an example of alternative splicing in gene selection for BCR?
the rearranged VDJ segment recombines first with Cμ segment creating the heavy chain μ for IgM, followed by Cδ segment creating the heavy chain δ for IgD
what is the reason for the alternative splicing seen in gene selection during synthesis of BCR?
in this way, both the IgM and IgD expressed on a B cell have the same VDJ
what are the 6 sources of BCR diversity?
1. multiple copies of germline VDJ • 2. Random recombination of gene segments • 3. imprecision during cut and paste • 4. junctional diversity • 5. random reassortment of any light chain with any heavy chain • 6. somatic hypermutation
what is junctional diversity?
addition of sequence at the splice junction between V_D or D_J gene segments
what is somatic hypermutation?
fine tuning change after mutation
what is the cause of imprecise recombination in BCR formation?
the precise positions at which the genes for the V and J or VDJ segments are joined are not constant
imprecise DNA recombination can lead to what?
changes in the amino acid at the junctions
where does insertion of a new piece of DNA at the junctions take place?
at the junction of new segments
what is TdT?
terminal deoxynucleotidyl transferase
what is affinity maturation?
when somatic hypermutation improves the affinity of the antibody to the epitope
what is somatic hypermutation?
change in nucleotide in the rearranged variable gene segment of the light and heavy chain mainly in the CDR regions
the maturation stages of B cell development can be identified by what?
changes in enzyme activitiy • CD marker expression • synthesis of the BCR
what is allelic exclusion?
in a single B cell only one set of genes is expressed either maternal or paternal
what is Heavy chain rearrangement in the Pro B Cell?
DJ joined in both the chromosomes. Then VDJ is formed in one of the chromosomes
where do B cells develop?
in the fetal liver and adult bone marrow
when does heavy chain rearrangement take place?
in the pro B cell
what happens durring Ig Gene expression in the Pre B Cell?
VDJ get joined to the HCμ. μ chain together with surrogate chain is expressed
what is the μ chain together with the surrogate chain in the pre-Bcell called?
pre-B cell receptor
at the pro B cell level in the bone marrow, gene rearrangement of the H chain start with what?
a union of the D and J genes in both chromosomes (maternal and paternal)
what are the genes need to complete IgM?
what happens if VDJCμ is productive- capable of being properly transcribed and translated?
further rearrangement of VDJ gene from the other chromosome is shut down, if not, the cell is given a second chance to use the other chromosome. if this fails, the cell dies by apoptosis
what is a surrogate light chain?
a false light chain
do the genes for VpreB and λ5 undergo rearrangement?
what do Igα and Igβ do in the pre-B cell?
singal the cell that has successfully rearranged its Ig H chain and has made functional μ chain to shut down further H chain rearragement
what is Bruton's tyrosine Kinase?
one of the enzymes involved in intracellular signalling by Igα/β
mutation in the Btk gene results in what?
lack of differentiation to proB cell level
what is the condition caused by deficiency or defect in Btk?
what happens if in the maturation of a B cell the cell is not self reactive?
alternative mRNA splicing of heavy chain gene transcripts then produces the δ and μ expressing both IgD and IgM
what happens once a functional pro-B cell receptor is produced?
rearrangement of the light chain genes start
which light chain genes rearrange first?
what is central tolerance?
negative selection of self reacting immature B cells
what is receptor editing?
alteration of speecificity: • further round of light chain (V and J) gene rearrangement
what happens when an immature B cell recognizes a multivalent self molecule?
DELETION: • clonal deletion or receptor editing --> apoptosis
what happens when an immature B cell recognizes soluble self molecules?
ANERGY: • migrates to the periphery
what happens when an immature B cell recognizes low affinity non cross linking self molecule?
IGNORANT: • migrates to periphery • Mature B cell is clonally ignorant
what happens to an immature be cell with no self reaction?
FUNCTIONAL: • it migrates to the periphery and becomes mature
do anergic B cells express IgD?
do clonally ignorant B cells express Ig?
yes, IgM and IgD
what is a clonally ignorant cell?
ligand is present but is not able to activate the cell
what are the cell stages of B cell maturation?
1. Stem Cell • 2. Early Pro-B cell • 3. Late pro-B cell • 4. Large Pre-B cell • 5. small pre-B cell • 6. immature B cell • 7. Mature B cell
what is the status of the H-chain genes in a stem cell?
what is the state of the L chain genes in a stem cell?
what is the state of surface Ig in a stem cell?
what is the state of H chain genes in an early pro-B cell
what is the state of L chain genes in an early pro-B cell?
what is the state of surface Ig in an early pro-B cell?
what is the state of the H chain genes in a late pro B cell?
what is the state of the L chain genes in a late pro-B cell?
what is the state of the surface Ig in a late pro-B cell?
what is the state of the H chain genes in a large pre-B cell?
what is the state of the L chain genes in a large pre-B cell?
what is the state of surface Ig in a large pre-B cell?
μ chain transiently at surface as part of pre-B cell receptor. mainly intracellular
when does the μ + surrogate arrive in B cell maturation?
at the large pre-B cell stage
what is the state of the H chain genes in a small pre-B cell?
what is the state of the L-chain genes in a small pre-B cell?
what is the state of the surface Ig in a small pre-B cell?
intracellular μ chain
at what stage in B cell maturation is the check to see if they recognize self antigens?
immature B cell stage
what is the state of the H chain genes in an immature B cell?
what is the state of the L chain genes in an immature B cell?
what is the state of surface Ig in an immature B cell?
IgM expressed on cell surface
what is the state of the H chain genes in a mature B cell?
what is the state of the L chain genes in a mature B cell?
what is the state of surface Ig in a mature B cell?
IgD and IgM made from alternatively spliced H-chain transcripts
what do naive B cells express on their surface?
IgM and IgD
what do plasma cells express on their surface?
plasma cells do not express surface Ig, but secrete Ig
what do memory cells express on their surface?
other Ig: • either IgG, IgA, or IgE
what is the clonal selection theory?
upon exposure to an antigen, a B cell with a BCR specific to that particular antigen proliferates to give rise to a clone of B cells expressing BCR of the same specificity
what happens in Ig class/isotype switch?
change of C domain, but not the VDJ because of alternative mRNA splicing
what does DNA recombination in isotype switch permit a cell to do?
enables the rearranged VDJ to be used with other heavy chain C chains
what is the first Ig produced after a B cell encounters an antigen?
IgM, followed by IgG or IgA with the same VDJ
what is affinity maturation?
mutation that takes place in the rearranged VDJ segment gives rise to antibodies with better affinity to epitopes
do antibodies produced in primary infection have more or less affinity for the epitope than Ab produced in subsequent infections?
what is detection of CD10/19/20 used for?
determine the developmental stage of leukemias and lymphomas of B cell origin
what does B cell coreceptor do?
increaes the sensitivity of B cell response to an antigen in the presence of complement activation and deposition of C3d
what is C3d?
a fragment of C3b of complement component
what are the 2 important subsets of B cells?
B2 • B1 (CD5+)
when do B2 cells develop?
when are B1 cells produced?
in fetal life
which type of B cell has a poorly understood developmental pathway?
which type of B cell comprises the majority of B cells?
What percentage of B cells are B1 cells?
where are B2 cells found?
in secondary lymphoid organs
where are B1 cells found?
in body cavities
which surface Ig do B2 cells express?
both sIgM and sIgD
which surface Ig do B1 cells express?
sIgM but little sIgD
what type of antigens do B2 cells respond to?
which type of antigens do B1 cells respond to?
carbohydrate antigens • T independent antigens
which B cells require T cell help?
which B cells do not require T cell help?
which B cells secrete mainly IgM?
B 1 cells
which B cells give rise to plasma cells that secrete IgM, IgG, and IgA?
which B cells leave memory?
which B cells leave little to no memory?
B cells develop where in the body?
fetal liver • adult bone marrow
stages of B cell differentiation are defined by what?
Ig gene rearrangement 'status' and expression of certain CD 10, 19, 20
what is essential to the clonal nature of immunity?
how many opportunities do B cells have to rearrange their antigen receptors?
what are the possible fates of self reacting immature B cells expressing only IgM?
1. allowed for receptor editing • 2. deleted, made anergic or ignorant
why are IgM and IgD expressed simultaneously on mature B cells?
due to differential RNA splicing
what is the function of CD79?
what does a B cell do upon an exposure to an antigen?
proliferates and differentiates into plasma cells and memory cells
what is class switch and what does it refer to?
class switching is isotype switching and refers to changes in CH gene selection but with no change in other genes (V domains or antigen specificity) by alternative RNA splicing
what makes up B cell co-receptor?
CD19 • CD21 • CD81
what are the two subsets of B cell types?
B1 • B2
What are immunoglobulins/antibodies?
glycoprotein molecules produced by plasma cells in response to an immunogen that can recognize the immunogen/antigen
what is myeloma?
a cancer that affects B cells, the immune cells responsible for the production of antibodies
from where do immunoglobulins derive their name?
the finding that when antibody-containing serum is placed in an electrical field the antibodies migrated with the globular proteins
the Ig molecule is made up of how many proteins?
4 peptide chains
what is the composition of the 4 peptide chains in an Ig?
2 heavy identical chains • 2 light identical chains
what are the regions present in Ig molecules?
the chains have variable region and constant region
what are VL and CL?
variable and constant region of the light chain
what are VH and CH?
variable and constant region of the heavy chain
what are responsible for the folding in the domains of an Ig?
what makes up an Ig?
1. 4 peptide chains with heavy and light chains with variable and constant regions • 2. hinge region • 3. domains folded by sulfide bonds • 4. oligosaccharides
what are Ig classes/isotypes?
5 different classes based on the differences in the amino acid sequences in the constant region of the heavy chain
what are the 5 different heavy chains that determine the Ig classes?
1. γ • 2. μ • 3. α • 4. δ • 5. ε
What Ig is associated with the γ chain?
heavy chain of IgG
what Ig is associated with the μ chain?
heavy chain of IgM
what Ig is associated with the α chain?
heavy chain of IgA
what Ig is associated with the δ chain?
heavy chain of IgD
what Ig is associated with the ε chain?
heavy chain of IgE
what is the difference between the IgG subclasses?
differ in amino acid sequence in their constant region of H chain: • 1. IgG1- gamma 1 heavy chains • 2. IgG2- Gamma 2 heavy chains • 3. IgG3- Gamma 3 heavy chains • 4. IgG4- Gamma 4 heavy chains
what is the difference between IgA Subclasses?
differ in aa sequence in their H constant region: • 1. IgA1 • 2. IgA2
what are the 2 types of L chains of Ig?
Kappa- κ • Lambda- λ
what is the difference between κ and λ L chains of Ig?
they differ in amino acid sequences in their constant region
what is the prevalence of κ and λ chains in Ig?
both types occur in all classes of Ig, but any one Ig molecule contains only one of them, either λ or κ
how many subclasses of IgG?
how many classes of IgA?
What is the organization of H2L2 structures?
2 identical L chains • 2 identical H chains • the H chain defines the class (and subclass) of the Ig produced
what is the functional organization of H2L2 structures?
1. variable N terminal regions define the antigen binding site • 2. constant regions of the heavy chains define the functions of the immunoglobulin
in humans, what is the ratio of immunoglobulins containing two kappa vs two lambda chains?
how can the distinct fragments of the heavy chains be isolated into distinct fragments?
what happens when you reduce and acidify immunoglobulin?
you get isolated chains separated at the sulfide bonds
what happens when you treat an immunoglobulin with papain?
you get papain fragments
what does the Fc region do?
determines the biological function of Ig
what does the Fc region of Ig bind to?
Fc receptors on: • 1. phagocytic cells • 2. NK cells • 3. eosinophils • 4. Mast cells • 5. complement C1q • 6. placental cells
what are the different kinds of Fc receptors on cells?
different Fc receptors on these cells for the different Ig classes: • FcγR- IgG • FcμR- IgM • FcαR- IgA • FcεR- IgE
why is an antibody able to bind a particular antigenic determinant?
because it has a particular combination of VH and VL
specificity of antigen binding is determined by what?
hypervariability regions within the variable region domain
how many hyper-variable regions per variable region?
each variable region has 3 hyper-variable regions also called what?
complementary determining regions (CDR)
how many CDR's per antigen binding site?
an antigen binding site is composed of three light chain CDR's and 3 heavy chain CDRs
different combinations of a VH and VL result in what?
antibodies that can bind a different epitope
what is the antigen binding region called?
how is variability distributed in V domains?
there are discrete regions of hypervariability in V domains
what are the positions of CDR in the 2-D and 3-D models of the light chain and heavy chain?
-CDRs are separated in the linear 2D model of the peptide chains • - the hypervariable regions of the light chain and heavy chain are brought together in the folded 3D form of the intact antibody molecule
together the CDRs constitute what?
the combining site, which is complementary to the epitope
the variability in CDRs provides what?
the diversity required for the function of antibodies of different specificities
what is affinity in an Ab/Ag interaction?
strength of interaction between one epitope and one epitope binding site (the region between the variable region of heavy chain and light chain)
what is avidity in Ag/Ab interaction?
strength of interaction of multiple epitopes on a multivalent antigen molecule such as a big protein and several epitope binding site
what are hinge options?
the ability of an antibody to bind more than one protein with variable spacing on the surface of a bacterium
what is the structure of IgG?
how do the subclasses of IgG differ?
number of disulfide bonds and length of the hinge region
which is the most versatile Ig molecule?
why is IgG isotype the most versatile immunoglobulin?
because it is capable of carrying out all of the functions of immunoglobulin molecules
what is the major Ig in serum?
how much of serum Ig is IgG?
which is the major Ig in the extravascular spaces?
what are the capabilities of IgG?
1. neutralization • 2. fixes complement • 3. binding to cells • 4. opsonization
what is neutralization by IgG?
inhibit binding of toxins or pathogens on target cells
do all subclasses of IgG fix complement?
not all subclasses fix complement equally well; IgG4 does not fix complement
which IgG does not fix complement?
which cells have Fc receptors for the Fc region of IgG?
1. macrophages • 2. monocytes • 3. PMNs • 4. NK cells
do all subclasses of IgG bind to cells?
not all subclasses bind equally well; • IgG2 and IgG4 do not bind Fc receptors
describe opsonization by IgG
IgG is a good opsonin. • a consequence of binding to the Fc receptors on PMN's, monocytes and macrophages is that the cell can now internalize the antigen better
what is the name for adaptive immune defense mediated by antibodies?
which is the only Ig that crosses the placental barrier?
what is transfer of IgG across the placental barrier mediated by?
receptor on placental cells for the Fc region of IgG
do all IgG subclasses cross the placental barrier?
not all subclasses cross equally • IgG2 does not cross well
which IgG does not cross the placental barrier well?
what is ADCC?
antibody dependent cell-mediated cytotoxicity
NK cells have Fc receptors for which IgG?
IgG1 and IgG3
binding of NK cells to human cells coated with IgG1 an IgG3 results in what?
ADCC targets what kind of cells?
tumor cells and virally infected human cells
why are tumor cells and virally infected human cells targeted by NK cells in ADCC?
they express antigens that are not found in normal cells
what are the steps of ADCC by NK cells?
1. antibody binds antigens on the surface of target cells • 2. Fc receptors on NK cell recognize bound antibody • 3. cross-linking of Fc receptors signals the NK cell to kill the target cell • 4. target cell dies by apoptosis
what are the features of the structure of IgM?
Pentamer (19s) • extra domain (CH4) • J chain
in what 2 configurations can IgM exist?
1. IgM normally exists as a pentamer (19S) in serum • 2. can exist as a monomer as antigen receptor on B lymphocytes
which is the third most common Ig in serum?
what is the valence of an Ig?
it's epitope binding capacity
what is the similarity between chains in IgM when it is in its pentameric form?
all heavy chains are identical • all light chains are identical
what is the valence of IgM in its pentameric form?
what are the extra peptide features of IgM?
1. extra domain on the μ chain (CH4) • 2. another protein covalently bound via S-S bond called the J chain
what is the J chain on IgM?
another protein covalently bound to IgM via S-S bonds
which chain functions in polymerization of the IgM molecule into a pentamer?
what is the first Ig to be synthesized by B cells during infection in adults?
what is the first Ig produced in fetal life?
in the newborn, an increased level of IgM is an indication of what?
in utero stimulation of the immune system by pathogens such as rubella virus, CMV, syphilis, toxoplasmosis
what are the pathogens that cause increased IgM in a newborn?
1. rubella virus • 2. cytomegalovirus • 3. syphilis • 4. toxoplasmosis
which is the first type of antibody to appear in the primary response, between IgG and IgM?
what happens to IgG levels in the secondary response (compared to the primary response)?
IgG: • 1. appears earlier • 2. shows a more rapid rise • 3. has higher final concentration
what would happen if at the time of the second exposure to Ag1, a second, non-cross reacting Ag2 was injected?
a primary response to Ag2 would occur while a secondary response to Ag1 was occuring
how can the IgM Fc region affect complement?
the IgM Fc region can bind and activate complement
how many antigen binding sites does IgM pentamer have?
how many Fc regions for complement binding does an IgM pentamer have?
which Ig has the most efficient complement fixation?
which Ig is most efficient at agglutinating antigens?
how is the response of IgM to T cell independent (carbohydrate) antigens?
how is the structure of surface IgM different than serum IgM?
1. exists as monomer • 2. lacks J chain • 3. extra 20 amino acids at the C terminal end to anchor it to the membrane
what is the function of cell surface IgM?
receptor for antigen on B cells
what is the structure of serum IgA?
what are the structural features of secreted IgA (sIgA)?
Dimer (11s) • J chain • secretory component
when IgA exists as a dimer, what is associated with it?
when IgA is found in secretions it also has, in addition to the J chain, what associated with it?
another protein called the secretory piece
what is IgA in secretions called?
where is most of IgA made?
in the plasma cell
unlike the remainder of the IgA which is made in the plasma cell, the secretory piece is made where? and when?
in the epithelial cells and is added to the IgA as it passes into the secretions
what is the function of the secretory piece?
the secretory piece helps IgA to be transported across mucosa and also protects it from degradation by enzymes in the mucosal secretions
during which part of secretion of sIgA is the secretory component added?
during trancytosis between the extracellular space and the lumen
for transcytosis and association with the secretory component to take place, the IgA dimer must bind what?
a membrane bound Fc receptor (poly-Ig receptor)
what is the second most common serum Ig?
IgA is the major class of Ig in what?
secretions: • 1. tears • 2. saliva • 3. colostrum • 4. mucus
how is IgA transferred from mother to child?
what type of immunity transfer is breast feeding?
passive transfer of immunity
since it is found in secretions, sIgA is important in what type of immunity?
local (mucosal) immunity
does IgA fix complement?
normally IgA does not fix complement unless aggregated
how does IgA function in mucosal immunity?
IgA inhibit by neutralizing adhesion of pathogens/toxins to epithelial cell on mucosal surface
what are the structural components of IgD?
monomer • tail piece
how does IgD exist?
IgD exists only as a monomer
is IgD found in serum?
IgD is found in low levels in serum
what is the role of serum IgD?
role in serum is uncertain
where is IgD primarily found?
on B cell surfaces
what is the function of B cell bound IgD?
receptor for antigen
which Ig's are found on the B cell surface?
IgD • IgM
IgD on the surface of B cells has what for anchoring to the membrane?
extra amino acids at C-terminal end
does IgD bind complement?
what are the structural components of IgE?
monomer • extra domain Cε4
which is the least common serum Ig?
why is IgE the least common serum Ig?
it binds very tightly to FcεR receptors on basophils and mast cells
IgE is primarily involved in what?
why is IgE involved in allergic reactions?
as a consequence of its binding to basophils and mast cells
does IgE fix complement?
IgE does not fix complement
Binding of IgE to mast cell surface receptors does what?
primes the cell to respond to allergen
introduction of allergen and its subsequent binding to IgE on a mast cell induces what?
crosslinking of IgE and clustering of Fc receptors
clustering of Fc receptors on a mast cell post introduction of allergen does what?
initiates a signal transduction event that stimulates the mast cell to degranulate
besides allergic reactions, what does IgE play a role in?
parasitic helminth infections
what are the functions of IgE?
allergic reactions • parasitic helminth infections
why is measuring IgE levels helpful in diagnosing parasitic infections?
because serum IgE levels rise in parasitic diseases
how does IgE help kill parasites?
eosinophils have Fc receptors for IgE and binding of eosinophils to IgE-coated helminthes results in release of granular contents which kill the parasite
which Ig's predominate in the blood?
IgM, IgG and monomeric IgA predominate in the blood
which are the major Ig's in the extracellular fluid?
IgG and monomeric IgA
which Ig predominates in the secretions?
where is IgE found?
IgE is associated with mast cells and is therefore found in the connective tissue beneath epithelial surfaces, particularly of the skin, respiratory tract and the GI tract
which Ig's are in the brain?
THE BRAIN IS DEVOID OF IMMUNOGLOBULIN
isotypes of Ig have variations in what?
the Fc region, constant heavy chain
what are allotypes of Ig?
alleles: • variations in the Fc region found in members of the same species
when is the allotype of Ig important?
tissue typing for transplantation
what are idiotypes of Ig?
variation in the variable region
what does the idiotype of an Ig determine?
what differentiating class of an Ig is present in all individuals of a species?
which differentiating class of an Ig is different alleles within a species?
which differentiating Ig class determines the antigen binding site?
What is the degree of neutralization functionality of IgM?
what is the degree of neutralization function of IgD?
what is the degree of neutralization function of IgG1?
what is the degree of neutralization function of IgG2?
what is the degree of neutralization function of IgG3?
what is the degree of neutralization function of IgG4?
what is the degree of neutralization function of IgA?
what is the degree of neutralization function of IgE?
which Ig's have + degree of neutralization function?
which Ig's have - degree of neutralization function?
IgD • IgE
which Ig's have +++ degree of neutralization function?
IgG1 • IgG2 • IgG3 • IgG4 • IgA
what is the degree of opsonization function of IgM?
what is the degree of opsonization function of IgD?
what is the degree of opsonization function of IgG1?
what is the degree of opsonization function of IgG2?
* req complement
what is the degree of opsonization function of IgG3?
what is the degree of opsonization function of IgG4?
what is the degree of opsonization function of IgA?
what is the degree of opsonization function of IgE?
which Ig's have - degree of opsonization function?
IgM • IgD • IgE
which Ig's have + degree of opsonization function?
IgG4 • IgA
which Ig's have ++ degree of opsonization function?
which Ig's have +++ degree of opsonization function?
what is the degree of sensitization for killing by NK cells function of IgM?
what is the degree of sensitization for killing by NK cells function of IgD?
what is the degree of sensitization for killing by NK cells function of IgG1?
what is the degree of sensitization for killing by NK cells function of IgG2?
what is the degree of sensitization for killing by NK cells function of IgG3?
what is the degree of sensitization for killing by NK cells function of IgG4?
what is the degree of sensitization for killing by NK cells function of IgA?
what is the degree of sensitization for killing by NK cells function of IgE?
which Ig's have - degree of sensitization for killing by NK cells function?
IgM • IgD • IgG2 • IgG4 • IgA • IgE
what is the degree of sensitization of mast cells function of IgM?
what is the degree of sensitization of mast cells function of IgD?
what is the degree of sensitization of mast cells function of IgG1?
what is the degree of sensitization of mast cells function of IgG2?
what is the degree of sensitization of mast cells function of IgG3?
what is the degree of sensitization of mast cells function of IgG4?
what is the degree of sensitization of mast cells function of IgA
what is the degree of sensitization of mast cells function of IgE?
which Ig's have - degree of sensitization of mast cells function?
IgM • IgD • IgG2 • IgG4 • IgA
which Ig's have + degree of sensitization of mast cells function?
IgG1 • IgG3
which Ig's have +++ degree of sensitization of mast cells function?
what is the degree of activation of complement system function of IgM?
what is the degree of activation of complement system function of IgD?
what is the degree of activation of complement system function of IgG1?
what is the degree of activation of complement system function of IgG2?
what is the degree of activation of complement system function of IgG3?
what is the degree of activation of complement system function of IgG4?
what is the degree of activation of complement system function of IgA?
what is the degree of activation of complement system function of IgE?
which Ig's have - degree of activation of complement system function?
IgD • IgG4 • IgE
which Ig's have + degree of activation of complement system function?
IgG2 • IgA
which Ig's have ++ degree of activation of complement system function?
which Ig's have +++ degree of activation of complement system function?
IgM • IgG3
what is the degree of transport across epithelium of IgM?
what is the degree of transport across epithelium of IgD?
what is the degree of transport across epithelium of IgG1?
what is the degree of transport across epithelium of IgG2?
what is the degree of transport across epithelium of IgG3?
what is the degree of transport across epithelium of IgG4?
what is the degree of transport across epithelium of IgA?
what is the degree of transport across epithelium of IgE?
which Ig's are not transported across epithelium?
IgD • IgG1 • IgG2 • IgG3 • IgG4 • IgE
which Ig's are transported across epithelium to some degree?
which Ig's are transported across epithelium A LOT?
what is the degree of transport across placenta of IgM?
what is the degree of transport across placenta of IgD?
what is the degree of transport across placenta of IgG1?
what is the degree of transport across placenta of IgG2?
what is the degree of transport across placenta of IgG3?
what is the degree of transport across placenta of IgG4?
what is the degree of transport across placenta of IgA?
what is the degree of transport across placenta of IgE?
what Ig's are not transported across placenta?
IgM • IgD • IgA • IgE
which Ig's are transported across placenta to some degree?
which Ig's are transported across placenta to a moderate degree?
IgG3 • IgG4 • (++)
which Ig's are transported across placenta A LOT?
what is the mean serum level (mg/mL) of IgM?
what is the mean serum level (mg/mL) of IgD?
what is the mean serum level (mg/mL) of IgG1?
what is the mean serum level (mg/mL) of IgG2?
what is the mean serum level (mg/mL) of IgG3?
what is the mean serum level (mg/mL) of IgG4?
what is the mean serum level (mg/mL) of IgA
what is the mean serum level (mg/mL) of IgE?
5 x 10^-5
what is an immunogen?
substance capable of inducing adaptive immune response
what is an antigen?
substance capable of being recognized by the adaptive immunity.
what is the relationship between antigens and immunogens?
All immunogens are antigens, but not all antigens are immunogens
what is an epitope?
the region(s) of the antigen in direct contact with the antibody, B-Cell Receptor, or T-Cell Receptor
what is a synonym for epitope?
how many epitopes are there per antigen?
there may be one or more epitopes per antigen
what is a hapten?
a small molecule which can function as an antigen, but by itself is incapable of inducing an immune response
is a hapten an immunogen?
what are the 3 types of antigen/immunogen receptor molecules?
1. BCR (b cell receptor) • 2. TCR (t cell receptor) • 3. MHC
of the 3 types of antigen/immunogen receptor molecules, which are surface immunoglobulins?
how many antigen recognition sites are there on a BCR?
two identical antigen recognition sites
how many antigen recognition sites are there on a TCR?
one antigen recognition site
where are MHC-I molecules expressed?
on all nucleated cells
where are MHC-II molecules expressed?
macrophages • dendritic cells • lymphocytes
which of the 3 types of antigen/immunogen receptor molecules is expressed on antigen presenting molecules?
which various antigens or sources of antigens are immunogens?
1. parasites • 2. foreign proteins • 3. bacteria • 4. viruses • 5. fungi
antigens are big molecules- however, the area that triggers the specific immunity is a small part, known as what?
how big is an epitope?
an epitope in a protein antigen could be as few as 20 amino acids long
what is the shape of an epitope?
could be linear, conformational
what type of cells recognize a conformational epitope?
BCR only, not TCR
what is the difference between a linear and conformational epitope?
in a conformational epitope, the sequence of amino acids is discontinuous, but they are brought into proximity by the protein's 3-D structure
what is a synonym for conformational epitope?
when is there cross-reaction between different antigens?
when a different antigen has one identical determinant or a similar determinant
when is there no reaction between different antigens?
when there is no structural similarity
what is the receptor/binding activity of a BCR?
what is the receptor/binding activity of a TCR?
TCR --> Ag/MHC
is MHC required for BCR?
is MHC required for TCR?
does a BCR bind soluble antigen?
does a TCR bind soluble antigen?
what is the chemical nature of BCR antigens?
protein • polysaccharides • lipids • nucleic acids
what is the chemical nature of TCR antigens?
proteins • some lipids, glycolipids
what type of epitope is recognized by BCR?
accessible, either linear or conformational
what type of epitope is recognized by TCR?
linear peptides (short)
what makes a good antigen/immunogen?
1. physical size : > --> better • 2. complexity: chemical composition and structural complexity • 3. solubility or degradability by antigen processing cells, macrophages, dendritic cells and B cells • 4. foreignness to the individual
what size are the best immunogens?
what is the minimum size for active immunogens (proteins)
how immunogenic is an immunogen that is <5-10kD?
minimally immunogenic, usually require carrier
what is an example of a <5-50kD immunogen that is minimally active and requires a carrier?
How do the categories of chemical compounds rank in terms of their immunogenicity based on complexity in descending order?
HIGH IMMUNOGENICITY: • 1. proteins and glycoproteins • 2. Polysaccharides • 3. nucleic acids, phospholipids • 4. haptens • LOW IMMUNOGENICITY:
are proteins and glycoproteins good immunogens?
how complex are proteins and glycoproteins in terms of their immunogenicity?
complex in composition and structure
can proteins and glycoproteins induce immunity?
can induce humoral and cell-mediated immunity
how complex are polysaccharides in terms of their immunogenicity?
repeating structures, generally low affinity
what type of response do polysaccharide immunogens elicit?
do polysaccharides stimulate a cell-mediated immune response?
cannot be processed and presented as linear epitopes for T cells, thus do not induce cell-mediated response
how foreign are nucleic acids and phospholipids in terms of their immunogenicity?
evolutionarily conserved; less foreign
how do nucleic acids and phospholipids become better immunogens?
conjugation with proteins or polysaccharides
how immunogenic are haptens?
insufficient in size to be immunogenic. need carrier
what examples of natural haptens?
hormones, lipids, simple sugars
what are examples of synthetic haptens?
chemicals, drugs (penicillin)
what types of drugs can act like haptens and be associated with severe, life threatening anaphylactic reactions?
antibiotics, particularly penicillins
how do penicillins act as haptens?
they form covalent bonds with proteins to produce protein-drug adducts that elicit an immune response (hypersensitivities) in some individuals
what are the 3 types of epitopes in a hapten-conjugate complex?
1. the pure hapten • 2. the pure antigen • 3. the hapten-antigen complex
how can a hapten be made immunogenic?
immunizing with a hapten-carrier conjugate
do identical twins recognize each other's proteins as foreign?
no. • they have the same genetic makeup and their immune systems would recognize eachother as self
what are examples of immunologically privileged anatomical sites (sequestration)?
corneal, spermatic, CNS cell antigens
What are the types of antigens?
1. mitogens • 2. superantigens • 3. T cell independent • 4. T cell dependent
mitogens are characterized by what?
the same epitope repeated many times
how many types of B cells can mitogens activate?
more than one B cell type/clone
are mitogens B cell monoclonal or polyclonal activators?
B cell polyclonal activators
what are superantigens?
antigens that can activate more than one type of T cell
are superantigens polyclonal/monoclonal B/T cell activators?
polyclonal T cell activators
what effect do superantigens have on the immune system?
cause hyper activation of the immune system
what is an example of excessive T cell activation having drastic effects?
toxic shock syndrome
what does an antigen being T cell independent vs. T cell dependent depend on?
whether an anigen can stimulate B lymphocytes with or without the help from T lymphocytes
How do superantigens induce activation of multiple types of T cells?
they are polyclonal stimulators of T cells, binding to the MHC-TCRβ (on the outside of the polypeptide of TCR) complex, without regard for antigen specificity
How much of CD4 T cells are activated by super antigens?
up to 20%
what is the result of a superantigen activating up to 20% of circulating CD4 T cells?
massive production of cytokines such as IL1, IL2, and TNFα which causes systemic shock
what are examples of conditions that are caused by superantigens?
food poisoning • toxic shock syndrome
what microbes cause food poisoning and/or toxic shock syndrome?
bacterial exotoxins: • staphylococcal • enterotoxins • staphylococcal toxic shock toxin • staphylococcal exfoliating toxin • streptococcal pyrogenic exotoxins
what forms a bridge between CD4 T cell's receptor and the MHC II molecule?
what do T cells do in response to a superantigen?
divide and differentiate into effector cells
what are T-independent antigens?
antigens which can directly stimulate B cells to produce antibody without the requirement for T cell help
do T independent antigens require to be presented by APC?
usually, T independent antigens are what?
mitogen and are resistant to degradation by antigen presenting cell
what are examples of T independent antigens?
pneumococcal polysaccharide • lipopolysaccharide • flagellar antigen
what are T dependent antigens?
antigens that require the help of T lymphocytes to activate be cells to produce antibody
are T dependent antigens degradable by antigen presenting cell?
what type of compounds are T dependent antigens?
in addition to size, molecular complexity and foreignness, immunogenicity of an antigen depends on what?
1. physical form • 2. degradability • 3. route • 4. dose • 5. adjuvant
which physical form of an antigen is more immunogenic, particulate or soluble?
particulate > soluble
why are particulate antigens more immunogenic than soluble ones?
particulate form are more easily taken up by antigen presenting cells
which physical form is more immunogenic, denatured or native?
denatured > native
what speed of release is important for immune response?
what are the relative immunogenicities of routes of administration?
subcutaneous > intraperitoneal > intravenous > intragastric
what is the limitation of the oral route of administration's immunogenicity?
oral route induces local mucosal immunity but not systemic immunity
what is low zone tolerance?
low doses appear to inhibit the specific antibody production
what is high zone tolerance?
very high doses of antigen inhibit immune responsiveness to a subsequent challenge
what is the effect of an adjuvant on immunogenicity?
substances mixed together with an antigen and enhance an immune response to an antigen
what is the difference between an adjuvant and a carrier molecule?
unlike carrier molecule an adjuvant does not form stable linkage with the antigen
what is an example of an adjuvant?
1. complete Freund's adjuvant • 2. aluminum hydroxide/aluminum phosphate
what is Complete Freund's Adjuvant?
water in oil emulsion containing killed mycobacteria
how does an adjuvant increase immunogenicity of an antigen?
1. insolubilize antigen for better phagocyte uptake • 2. insolubilize antigen for gradual release over time in lipid emulsions called liposomes with delayed time release of antigen • 3. stimulating the influx of phagocytic cells or other immune cells to the site
some adjuvants contain mycobacterial components capable of stimulating what?
the innate immunity- acitvation of macrophages
what can inflammation be thought of as?
a regulatory event aimed at mobilizing various innate immune effectors and trafficking them to the anatomic location where they can be most effective
what is the etymology of inflammation?
latin: inflammare- to set on fire
inflammation is initiated by the presence of what?
infectious agents • tissue damage • self (auto) antigens (autoimmunity)
in inflammation an innate or adaptive immune action?
combined action of several immune responses of both innate and specific immunity
inflammation leads to what?
1. vascular dilation/ increased vascular permeability • 2. accumulation of inflammatory cells • 3. destruction of initiating agent • 4. tissue repair • 5. tissue damage/scarring
what are the symptoms of inflammation?
rubor • tumor • calor • dolor • functio laesa
what are the cellular players in acute inflammation?
tissues mast cell • neutrophil • macrophage
what cells, in addition to the cellular players in acute inflammation, may also be found at site of inflammation?
eosinophils • basophils
what are the functions of tissue mast cells in acute inflammation?
release of histamine and other mediators
what are the functions of neutrophils in acute inflammation?
phagocytosis and killing
what are the functions of macrophages in acute inflammation?
phagocytosis and killing • antigen presentation
what are the functions of eosinophils in acute inflammation?
killing of parasites
inflammatory stimuli do what?
1. activate the complement system • 2. degranulate mast cells • 3. acitvate macrophages • 4. activate coagulation system
inflammatory stimulia activate the complement system, degranulate mast cells, activate macrophages and coagulation system leading to the production of what?
bradykinin, which increases vasodilation
in response to inflammatory stimuli, platelts are a mojor component of clotting, releasing what?
prostaglandins • hydrolytic enzymes • growth factors • other mediators that stimulate various cell types to contribute to antimicrobial defense, wound healing, and inflammation
microbes and/or their products that enter through a breach in the dermis induce what?
phagocytes to secrete pro-inflammatory cytokines (IL1, TNFα), also activate complement leading to the expression of adhesion molecules by vascular endothelium
the net movement of WBC's from circulation into tissue is called what?
what are the steps of extravasation?
1. Rolling Adhesion • 2. Firm Adhesion (tethering and tight binding, margination) • 3. diapedesis (transendothelial migration) • 4. Migration toward the site of infection
Extravasation is driven by what compounds?
TNFα • IL1 • IL8 • C3a • C5a
how does rolling in extravasation work?
1. rolling uses selectins • 2. rolling is a low affinity adhesion • 3. E-selectin on endothelium bind to mucin like adhesion molecule on the phagocytic membrane briefly. • 4. force of blood moves rolling on
what are the proteins that bind in rolling during extravasation?
E-selectins on endothelium bind to mucin-like adhesion molecules (selectins/Sialyl Lewis sugars) on the phagocytic membrane briefly
what force causes rolling during extravasation to move on?
describe activation by chemoattractants during extravasation
chemokines released during inflammation stimulate conformational change in integrin molecules in phagocytic membrane that incresae their affinity for ICAM adhesion molecules on the endothelium
what are the chemokines released during inflammation that stimulate conformational change in integrin molecules in phagocytic membrane that increase their affinity for ICAM adhesion molecules on the endothelium?
IL-8 • C5a
to what family of compounds does ICAM belong?
what proteins are associated with tethering and tight binding during extravasation?
what is LFA?
lymphocyte function-associated antigen 1
what types of adhesions are formed in tethering and tight binding during extravasation?
firm adhesion to ICAMS
what is diapedesis?
diapedesis is mediated by what?
PECAM, now renamed CD31
what is PECAM?
platelet endothelial cellular adhesion molecule
where is CD31 expressed?
on endothelial cells and neutrophils
what happens to endothelial expression of E and P selectins under the influence of inflammatory stimuli?
endothelial expression of E and P selectins increases
to what family of compounds does LFA-1 belong?
part of the integrin family of leukocyte adhesin molecules
What is CD18?
common β chain of the leukocyte integrins
what does absence of CD18 cause?
leukocyte adhesion deficiency disease
what cytokine released by macrophages upregulate the expression of P selectin on endothelial cells?
what do P and E selectin do?
together E and P selectin slow the motion of leukocytes through the bloodstream by causing them to roll along the endothelial surface, allowing other molecules to interact with the slowed leukocytes to stop them and promote their movement into the tissues.
what compounds stimulate E and P selectin expression?
IL-1 • LPS • TNFα
what is LPS a component of?
the membranes of many gram negative bacteria
what do LPS binding proteins on macrophages do when they come into contact with their ligand?
stimulate macrophages to release inflammatory cytokines
Both E and P selectins are known to bind with what?
Sialyl-Lewis x like glycans
where are Sialyl-Lewis x-like glycans expressed?
in relatively high numbers by circulating leukocytes
in addition to Sialyl Lewis glycans, what else does P selectin bind?
P-selectin glycoprotein ligand-1 (PSGL-1)
where is PGSL-1 expressed?
modestly expressed on human leukocytes
leukocyte recruitment by E and P selectin is analogous to what?
throwing a tennis ball at a velcro surface
tight adhesion to the rolling leukocyte is performed by what?
what does ICAM-1 bind to?
integrins LFA-1 and CR3 on the leukocyte surface
what does ICAM-1 do?
binds to the Integrins LFA-1 and CR3 on the leukocyte surface and arrests the motion of the rolling leukocyte.
why does ICAM-1 stop the rolling leukocyte?
stopping the leukocyte allows it to enter the tissues by secreting proteases to breach the endothelial basement membrane
what is the acute phase response?
physiological processes that occur during inflammation or tissue damage, triggered by IL-1, IL-6, TNFα
which cytokines trigger the acute phase response?
IL-1 • IL-6 • TNF-α
on what systems do IL-1, IL-6, and TNFα act during the acute phase response?
hypothalamus • bone marrow • liver
what does the acute phase response cause by acting on the hypothalamus?
what does the acute phase response cause by acting on the bone marrow?
stem cell differentiation and proliferation
what does the acute phase response cause by acting on the liver?
increase production of acute phase proteins
what are the purposes of the acute phase response?
- provides replenishment of cells and acute phase proteins used during an inflammation response • - increase metabolic activity
what are acute phase proteins?
heterogenous group of serum proteins that increase during inflammation
what do acute phase proteins do?
replace exhausted components and reinforce innate defenses against infection
what are the important acute phase proteins?
1. C-reactive protein • 2. mannose-binding lectin • 3. complement • 4. fibrinogen
what is CRP?
a protein found in the blood, the levels of which rise in response to inflammation
what does CRP do?
1. acts as an opsonin AND • 2. it binds to phosphocholine expressed on the surface of dead or dying cells (and some types of bacteria) in order to activate the complement system via the C1q complex (classical pathway in the absence of antibody)
what are the relative levels of CRP and MBL in the plasma?
the levels of CRP and MBL are low in the plasma, but levels can increase by up to 1000 fold during the peak of the acute phase response
when is the peak of the acute phase response?
about 2 days after its start
CRP and MBL both bind to what?
distinct structures that are common features of pathogens and not features of human cells
what is the clinical application of CRP?
levels of CRP are routinely measured in clinical diagnostic laboratories to indicate an acute inflammation
what does MBL do?
acts as opsonin and triggers complement activation via lectin pathway
what does fibrinogen do?
plays a role in blood clotting, which limits the spread of pathogens
IL1/IL6/TNFα elicit what acute phase response in the liver?
acute phase proteins (CRP, MBL)--> activation of complement/opsonization
IL1/IL6/TNFα elicit what acute phase response in the bone marrow endothelium?
neutrophil mobilization --> phagocytosis
IL1/IL6/TNFα elicit what acute phase response in hypothalamus?
increased body temperature --> decreased viral and bacterial replication
IL1/IL6/TNFα elicit what acute phase response from fat, muscle?
protein and energy mobilization to generate increased body temperature--> decreased viral and bacterial replication
what do pyrogens do?
increase body temperature
what is the purpose of fever?
1. increase metabolic activity • 2. inhibit multiplication of certain bacterial and viral agents • 3. human cells become more resistant to TNF-α
what does the acute phase reponse do to the supply of the recognition molecules of innate immunity?
increases the supply of the recognition molecules of innate immunity
what do bacteria do to induce synthesis of acute-phase proteins?
bacteria induce macrophages to produce IL-6, which acts on hepatocytes to induce synthesis of acute-phase proteins
what does the liver do in response to IL-6?
synthesize CRP, MBL, fibrinogen
what does CRP synthesized by the liver do to bacteria?
CRP binds phosphocholine on bacterial surfaces, acting as an opsonin and as a complement activator
what does MBL do to bacteria?
MBL binds to carbohydrates on bacterial surfaces, acting as an opsonin and as a complement activator
when does adaptive immunity play a role in inflammation?
in chronic inflammation: • non-digestible foreign material • chronic damage
what are the causes of chronic inflammation?
1. persistent infections and/or infections with resistant microorganisms such as mycobacterium • 2. autoimmune disease or malignancies (first response, acute followed by chronic) • 3. response to 'un-digestible' foreign material
does chronic inflammation involve innate or adaptive immunity?
what are the major cellular actors in chronic inflammation?
macrophages • Th1 (CD4) lymphocytes
what do macrophages do in chronic inflammation?
continue to produce pro-inflammatory cytokines (TNFα, IL-1, IL-8) and seek help from Th1
what do Th1 (CD4) lymphocytes do in chronic inflammation?
secrete several cytokines
what do IFNγ and CD40 ligand do in chronic inflammation?
regulate and strengthen the intracellular killing by macrophages and neutrophils
what does the secretion of TNFα, IL1, and IL8 by activated macrophages do in chronic inflammation?
promote recruitment of inflammatory cells to the area
how do Th1 and macrophages interact during chronic inflammation?
1. Th1 cell and infected macrophage come together • 2. T cell binds to and activates macrophage • 3. killing of intravesicular bacteria
when do granuloma form?
when an intracellular pathogen resists elimination even after receiving help from CD4 Th1
what do Th1 cells do when a pathogen resists intracellular killing?
play an important role in fighting such infections by producing different sorts of cytokines which bring more help to the macrophages
what are conditions in which granuloma form?
MTB • Leishmania
what cells make up and surround a granuloma?
macrophages make up the bulk of a granuloma and lymphocytes surround it
which type of inflammation is pyogenic, acute or chronic?
which type of inflammation is granulomatous, acute or chronic?
what are the typical triggers for acute inflammation?
what are the typical triggers for chronic inflammation?
mycobacterial infecton • hepatitis B
what are the initiating cells in acute inflammation?
mast cells • macrophages
what are the initiating cells in chronic inflammation?
what are the effector cells in innate system during acute inflammation?
what are the effector cells in the innate system during chronic inflammation?
macrophage • NK cell
what are the effector cells in the adaptive system during acute inflammation?
what are the effector cells in the adaptive system during chronic inflammation?
what are the mediators of acute inflammation?
complement, • GM-CSF, • TNF, • chemokines
what are the mediators of chronic immunity?
TNF • IL-12 • IL-18 • IFNγ • chemokines
what are the systemic effects of acute inflammation?
pus formation, abscesses
what are the systemic effects of chronic inflammation?
granuloma may be present
What happens in local infection with gram-negative bacteria?
1. macrophages activated to secrete TNF-α in the tissue • 2. Increased release of plasma proteins into tissue. Increased phagocyte and lymphocyte migration into tissue. Increased platelet adhesion to blood vessel wall • 3. phagocytosis of bacteria. local vessel occlusion. containment of infection. Antigens drain or are carried to local lymph node. • 5. survival. stimulation of adaptive immune system.
what happens in systemic infection with gram-negative bacteria?
1. macrophages activated in the liver and spleen secrete TNF-α into the bloodstream • 2. systemic edema causes decreased blood volume, hypoproteinemia, and neutropenia, followed by neutrophilia. decreased blood volume causes collapse of vessels. • 3. disseminated intravascular coagulation leads to wasting and multiple organ failure: septic shock. • 4. death
what do vascular endothelial cells make in response to TNF-α and what does it do to blood?
platelet activating factor, which triggers blood clotting and blockage of the local blood vessels.
what is the benefit of PAF released in response to TNFα by vascular endothelial cells?
restricts the leakage of pathogens into the circulation and prevents disseminated infection.
infection of the blood is known as what?
mutation of what has been linked to development of septic shock in patients?
mutation of TLR4 (a receptor for LPS on phagocytic cells)
What are the 3 classes of cellular effectors?
1. Degranulating Cells • 2. NK Cells • 3. Phagocytic Cells
What cells make up the degranulating cellular effectors of the innate immune system?
Mast Cells • Eosinophils
What cell line gives rise to NK Cells?
with what degree of specificity do NK cells kill?
do NK cells participate in innate or adaptive immunity?
lymphoid line, but part of innate immune system
what do NK cells target?
intracellular pathogens • tumor cells
what do phagocytic cells target?
what cells make up the phagocytic cellular effectors of the innate immune system?
neutrophils (PMNs) • monocytes/macrophages
part of the inflammatory response is the recruitment of what type of cells (the main line of defense in the non-specific immune system) to site of infection?
polymorphonuclear • eosinophils • macrophages
what are LAK cells?
Lymphokine Activated Killer Cells
what do NK and LAK cells do?
NK and LAK cells can nonspecifically kill virus infected and tumor cells
what do PMN cells do once they are recruited to the site of infection?
1. they phagocytose invading organisms and kill them intracellularly • 2. they contribute to collateral tissue damage that occurs during inflammation
what is the function of tissue macrophages and newly recruited monocytes which differentiate into macrophages in innate immunty?
1. phagocytosis and intracellular killing of microorganisms • 2. macrophages- contribute to tissue repair and act as antigen-presenting cells, which are required for the induction of specific immune responses
how do mast cells and eosinophils function in the innate immune response?
1. have proteins in granules that are effective at helping to recruit and enhance ann immune response • 2. eosinophils- killing certain parasites
where are mast cells found?
found posted throughout the body tissue
Mast cells can be stimulated to degranulate by what?
1. direct injury/ trauma • a. physical • b. chemical • 2. cross linking of IgE receptors • 3. activated complement proteins • a. C3a • b. C5a
what are the forms of chemical direct injury that cause mast cells to degranulate?
1. opioids • 2. alcohols • 3. certain antibiotics (polymyxins)
what are the inflammatory mediators released by the degranulation of mast cells?
1. histamine • 2. platelet activating factor • 3. prostaglandins • 4. leukotrienes
the degranulation of mast cells results in what?
1. recruitment of immune cells • 2. increase in vasopermeability
where are eosinophils found?
found circulating or in tissue
how are eosinophils recruited to the site of infection?
get recruited to the site of infection by cytokines
Eosinophils have receptors for which complement product?
what does C3b do to eosinophils?
what types of cells are targeted by eosinophils?
how do eosinophils kill big parasites?
1. producing oxygen radicals • 2. forming pores on target cells
are eosinophils phagocytic?
may be phagocytic and assist in clearing of foreign material at the site of injury or infection
how do eosinophils stain?
stain with acid dyes
chemotaxis of eosinophils to sites of infection is in response to what?
cytokines: • - IL8 • - Others belonging to chemokine family CXC and CC
NK cells participate in the recognition and killing of what target cells?
damaged or altered self cells • virally infected cells
what is the activation state of circulating NK cells?
circulate in partially activated state
what are the 2 mechanisms by which killing by NK is mediated?
1. secretion of perforins and granzymes lead to apoptosis of target cells • 2. FAS ligand mediated 'apoptosis'
what is the most important cytokine produced by NK cells?
what are the CD markers present on NK cells?
CD16 • CD56
why do NK cells respond quickly to infection?
because they circulate in partly activated state, as seen from their large size and their cytoplasmic granules loaded with toxic effector molecules
what does stimulation of NK cells with IFN-α and IFN-β favor?
the development of the cell's killer functions
what does stimulation of NK cells with IL-12 favor?
the production of cytokines
what is the principal cytokine released by NK cells?
IFN-γ/ type II interferon
what is a major function of IFN-γ?
to activate macrophages
what are the receptors on NK Cells?
1. KAR- Killer activating receptor • 2. KIR- killer inhibiting receptor
what ligands on target cells are recognized by NK cells?
KAL- Killer activating ligand
what are some examples of KAL?
viral antigens • tumor antigens (stress protein) • MICA, MICB
killing by NK cells is regulated by binding of what to what?
KAR to KAL • KIR to MHC I
if a target cell expresses MHC I, will it be killed by NK or LAK cells?
no • MHC I binds Killer Inhibiting Receptor
what types of cells express MHC-I?
normal cells constitutively express MHC-I molecules on their surface
how do viruses and tumor affect MHC-I?
virus infected and malignant cells down regulate expression of class I MHC
Infection of cells may lead to the surface expression of what?
in response to viral infection, host cells may express what?
stress molecules: • MICA and MICB • and reduce surface expression of MHC-I
what are MICA and MICB?
MHC class I chain-related Genes
expression of MICA and MICB can be detected by what?
NK cells that seek to eliminate virally infected cells
what happens if both KIR and KAR on the NK cell are bound?
if insufficient KIR-MHC-I binding occurs, the NK cell will proceed to kill the target host cell. • sufficient binding by KIRs will override the KAR kill signal, sparing the life of the host cell
where are the MICA and MICB genes located?
within the HLA class I region of chromosome 6
are MICA and MICB similar to HLA class I genes?
their organization, expression and products differ considerably from classical HLA class I genes.
MICA and MICB are considered to be markers of what?
stress in the epithelia
what do MICA and MICB act as?
ligands for cells expressing a common activatory natural killer cell receptor • ---KALs---
is the FasL on the NK cell or the target cell?
the NK cell
is the Fas Receptor on the NK cell or the target cell?
what are the 2 NK cell killing mechanisms?
1. Granzymes • 2. FasL/FasR
what is the mechanism of cell death induced by NK cells?
what cell is responsible for phagocytosis of debris generated by NK cell killing?
Absent NK activity is a component of what disease?
immunodeficiency disease Chediak-Higashi syndrome
what are the professional phagocytic cells?
polymorphonuclear neutrophils • mononuclear monocytes/macrophages
which class of professional phagocytic cell are granulocytes?
which class of professional phagocytic cells are agranulocytes?
do professional phagocytic cells circulate in blood?
PMN- circulate in blood • monocytes- circulate in blood • macrophages-reside in tissues
which of the professional phagocytic cells is more committed to phagocytic activity?
PMNs- mainly phagocytic • Mononuclear monocytes- have function other than phagocytosis
what are the functions of mononuclear monocytes/macrophages other than phagocytosis?
1. produce inflammatory cytokines • 2. clear debris and damaged tissue • 3. link innate to adaptive immunity
what is the lifespan of the professional phagocytic cells?
PMN's live <2days • MM/M's live months-years
what are the inflammatory cytokines produced by MM/M's
IL8 • IL1 • IL6 • TNFα
what is the morphology of PMN's?
variable and irregular shape of nucleus, contain granules
when are PMN's found in the tissues?
not found in healthy tissue, but when there is infection they enter tissue
what calls the PMN's to enter the tissues?
cytokines produced by the macrophages
which professional phagocytic cells set the stage for tissue repair?
which professional phagocytic cells clear tissue of products of inflammation and of remaining microbes?
What are the 2 major mechanisms by which immune cells recognize pathogens in innate immunity?
1. Pattern Recognition Receptors (PRR) • 2. Pathogen Associated Molecular Patterns (PAMP)
where are PRR's found?
on the surface of immune cells and soluble molecules
what are some examples of cellular PRR's?
1. Toll Like Receptors (TLR's) • 2. Complement Receptors (CR3 and CR4) • 3. Mannose Receptor • 4. Glucan Receptor • 5. CD14, LPS Receptor • 6. Receptor/Scavenger Protein
what is an example of a soluble PRR?
where are PAMP's found?
on the surfaces of microbes or microbial products
what are examples of PAMP's?
1. LPS of gram negatives • 2. Lipoteichoic acid of gram positives • 3. Lipoarabinoman of acid fast bacteria • 4. Mannose in glycolipids and glycopeptides (surface antigens) • 5. N-Formyl methionine peptides (soluble factor) • 6. dsRNA, ssDNA of viruses • 7. bacterial and viral unmethylated CpG DNA • 8. Bacterial Flagellin • 9. Glucans from fungal cell walls
which PAMP is associated with gram negative bacteria?
which PAMP is associated with gram positive bacteria?
Lipoteichoic acid • peptidoglycan
which PAMP is associated with acid fast bacteria?
which PAMP's are assciated with surface antigens?
mannose in glycolipids and glycopeptides (surface antigens)
which PAMP is evidence of prokaryotic proteins?
what is innate immunity designed to recognize?
molecules shared by groups of related microbes that are essential for the survival of those organisms and are not found associated with mammalian cells.
what are PAMP's?
unique molecules shared by groups of related microbes that are essential for the survival of those organisms and are not found associated with mammalian cells
what molecules on human cells can act as PAMP's?
DAMP's (Damage Associated Molecular Pattern)
how do toll like receptors sense infections?
with a horseshoe shaped structure- transmembrane polypeptides with pathogen recognition domain and a signalling domain
where might TLR's be expressed?
1. cell surface • 2. endosomes in the cytoplasm
what are the structural variations possible in TLR's?
1. single polypeptide • 2. homodimer • 3. heterodimer
which TLR is typically found as homodimer?
which TLR is typically found as heterodimer?
what are the ligands of the TLR1:TLR2 heterodimer?
Lipopeptides • GPI
what are the microorganisms recognized by TLR1:TLR2 heterodimer?
Bacteria • Parasites like trypanosomes
what cells carry the TLR1:TLR2 heterodimer?
monocytes • dendritic cells • eosinophils • basophils • mast cells
what are the ligands of the TLR2:TLR6 heterodimer?
lipoteichoic acid • zymosan
what are the microorganisms recognized by the TLR2:TLR6 heterodimer?
gram-positive bacteria • yeasts (fungi)
what are the cells carrying the TLR2:TLR6 heterodimer?
monocytes • dendritic cells • eosinophils • basophils • mast cells
what is the ligand of TLR3?
what microorganisms are recognized by TLR3?
viruses (west nile)
what cells carry TLR3?
what is the ligand of the TLR4:TLR4 homodimer?
what microorganisms are recognized by the TLR4:TLR4 homodimer?
what cells carry the TLR4:TLR4 homodimer?
macrophages • dendritic cells • mast cells • eosinophils
what is the ligand of TLR5?
what microorganisms are recognized by TLR5?/
motile bacteria havign a flagellum
what cells carry TLR5?
what is the ligand of TLR7?
what microorganisms are recognized by TLR7?
viruses like HIV
what cells carry TLR7?
plasmacytoid dendritic cells • NK cells • eosinophils • B cells
what is the ligand of TLR8?
what microorganisms are recognized by TLR8?
viruses like influenza
what cells carry TLR8?
what is the ligand of TLR9?
unmethylated CpG-rich DNA
what microorganisms are recognized by TLR9?
Bacteria • viruses like herpes
what cells carry TLR9?
plasmacytoid dendritic cells • B cells • eosinophils • basophils
what is the ligand and microorganism of TLR10 homodimer and heterodimers with TLR1 and TLR2?
which cells carry TLR10?
plasmacytoid dendritic cells • basophils • eosinophils • B cells
what TLRs are carried by NK cells?
TLR3 • TLR7 • TLR8
what TLRs are carried by monocytes?
TLR1:TLR2 • TLR2:TLR6
what TLRs are carried by dendritic cells?
TLR1:TLR2 • TLR2:TLR6 • TLR4:TLR4
what TLRs are carried by eosinophils?
TLR1:TLR2 • TLR2:TLR6 • TLR4:TLR4 • TLR7 • TLR9 • TLR10 • TLR10:TLR1 • TLR10:TLR2
what TLRs are carried by basophils?
TLR1:TLR2 • TLR2:TLR6 • TLR9 • TLR10 • TLR10:TLR1 • TLR10:TLR2
what TLRs are carried by mast cells?
TLR1:TLR2 • TLR2:TLR6 • TLR4:TLR4
what TLRs are carried by macrophages?
what TLRs are carried by plasmacytoid dendritic cells?
TLR7 • TLR9 • TLR10 • TLR10:TLR1 • TLR10:TLR2
what TLRs are carried by intestinal epithelia?
what TLRs are carried by B cells?
TLR7 • TLR9 • TLR10 • TLR10:TLR1 • TLR10:TLR2
which TLRs are found on cell surfaces?
TLR1:TLR2 • TLR2:TLR6 • TLR5 • TLR4
which TLRs are found inside the cytoplasm in endosome?
TLR7 • TLR8 • all the TLRs that recognize viral nucleic acids
What are the 2 possible fates of PRR+PAMP (danger signal)?
1. phagocytosis and killing • 2. cytokine production (inflammatory cytokines)
what do SOS signals include?
PAMP containing peptides released by bacteria • clotting system peptides • complement products • cytokines released from tissue macrophages that have encountered bacteria
phagocytic cells have what receptors on their cell membranes through which infectious agents bind to the cells?
1. complement receptors • 2. scavenger receptors • 3. toll like receptors
which component of complement do phagocytic cells have a receptor for?
binding of C3b coated bacteria to the receptor on phagocytic cells results in what?
enhanced phagocytosis and stimulation of the respiratory burst
what do scavenger receptors on phagocytic cells bind to?
a wide variety of polyanions on bacterial surfaces, resulting in phagocytosis of the bacteria
binding of infectious agents via toll like receptors on phagocytic cells results in what?
phagocytosis and the release of inflammatory cytokines by the phagocytes
what are the inflammatory cytokines released by phagocytic cells in response to TLR binding?
IL1 • TNFα • IL6
how does the Fc receptor work in adaptive initiation?
bacteria with IgG antibody on their surface have the Fc region exposed and this part of the Ig molecule can bind to the receptor on phagocytes
binding of IgG coated bacteria to Fc receptors on phago cytic cells results in what?
enhanced phagocytosis and activation of the metabolic activity of phagocytes (respiratory burst)
what does PAMP-PRR engagement do to phagocytes?
activates phagocytes to ingest and degrade the microbes
what happens in phagocytosis of a bacterium?
1. attachment of bacterium • 2. phagocyte begins to extend pseudopods around the bacterium • 3. pseudopods surround and engulf the bacterium • 4. bacterium is enclosed in a phagosome • 5. granules or lysosomes of the phagocyte fuse with the phagosome and empty their contents • 6. result is beacterium engulfed in phagolysosome which contains the contents of the granules or lysosomes
sensing of LPS by TLR4 on macrophages leads to what?
activation of the transcription factor NFκB and the synthesis of inflammatory cytokines
what does NFκΒ do in the nucleus of a macrophage?
activates transcription of genes for inflammatory cytokines, which are synthesized in the cytoplasm and secreted via the ER
PRR+PAMP sends signaling --> what?
what are the steps in phagocytosis by PMN's?
1. bacterium is phagocytosed by neutrophil • 2. phagosome fuses with azurophilic and specific granules • 3. pH of phagosome rises, antimicrobial response is activated, bacterium is killed • 4. pH of phagosome decreases, fusion with lysosome allows acid hydrolases to degrade the bacterium completely • 5. neutrophil dies by apoptosis and is phagocytosed by macrophage
why do neutrophils die?
the mature neutrophil cannot replenish its granule content, so once they are used up the neutrophils die by apoptosis and are cleared by macrophages
what do the contents of neutrophils' granules kill?
- microbes intracellularly during phagocytosis • - released extracellularly where they kill not only microbes but also surrounding cells and tissue
what are the 2 major types of neutrophil granules?
1. primary (azurophil) • 2. secondary (specific)
what are the contents of a primary granule in a neutrophil?
1. proteases • a. elastase • b. cathepsin G • 2. hydrolases • 3. myeloperoxidase • 4. defensins • 5. lysozyme • 6. BPI (bactericidal permeability increasing protein)
what keeps the contents of a primary granule inactive in a resting neutrophil ?
what are the contents of a secondary granule in a neutrophil?
1. lactoferrin • 2. lysozyme • 3. collagenase • 4. components of the NADPH oxidase system
what does BPI do?
binds to LPS and kills gram negative bacteria
what 2 mechanisms make up intracellular killing in neutrophils?
1. preformed compounds • 2. production of antimicrobial compounds
do preformed compounds in intracellular killing by neutrophils require oxygen?
no they are oxygen independent
where are preformed compounds in intracellular killing in neutrophils stored?
they are stored in cytoplasmic granules
do the antimicrobial compounds produced in intracellular killing in neutrophils require oxygen?
they are oxygen dependent • RESPIRATORY BURST
what is bystander damage?
when compounds involved in intracellular killing by neutrophils are released to the surrounding tissue and cause damage
what are the oxygen independent preformed microcidal compounds found in neutrophils that damage microbial membranes?
1. Cathepsin G • 2. Low molecular weight defensins • 3. high molecular weight cationic proteins • 4. bactericidal permeability • 5. BPI
what are the oxygen independent microcidal compounds in neutrophils that split mucopeptide in bacterial cell walls?
what oxygen independent microcidal compounds in neutrophils complex with iron?
what oxygen independent microcidal compounds in neutrophils digest killed organisms?
proteolytic enzymes • other hydrolytic enzymes
how does lactoferrin exert its microcidal effect?
it chelates iron, which deprives bacteria of this required nutrient
which intracellular killing mechanism is more efficient, oxygen dependent or independent?
can patients with defects in oxygen dependent mechanism of itnracellular killing still kill bacteria?
patients with defects in oxygen dependent microcidal pathways have what problem?
they are more susceptible and get more serious infections
What are three reactions involving superoxide and hydrogen peroxide in the oxygen dependent respiratory burst?
how is glucose metabolized during phagocytosis?
via the Pentose phosphate pathway and NADPH is formed
what is the respiratory burst
the increase in glucose and oxygen consumption during phagocytosis
what is the consequence of the respiratory burst?
a number of oxygen containing compounds are produced which kill the bacteria being phagocytosed
what are the 2 types of oxygen dependent intracellular killing?
1. oxygen dependent myeloperoxidase-independent intracellular killing • 2. oxygen-dependent myeloperoxidase-dependent intracellular killing
what is the role of cytochrome B in oxygen-dependent myeloperoxidase-independent intracellular killing?
cytochrome B, which was part of the specific granule, combines with the plasma membrane NADPH oxidase and activates it
what does NADPH oxidase do?
the activated NADPH oxidase uses oxygen to oxidize the NADPH, resulting in the production of a superoxide ion, some of which is converted to H2O2 and singlet oxygen by superoxide dismutase
what is the product of the reaction between H2O2 and superoxide?
hydroxyl radical and singlet oxygen
what are the toxic oxygen species produced in oxygen dependent myeloperoxidase independent intracellular killing?
O2- (superoxide ion) • H2O2 • OH* (hydroxyl radical)
when is myeloperoxidase released into the phagolysosome in oxygen dependent myeloperoxidase dependent intracellular killing?
as the azurophilic granules fuse with the phagosome
what does myeloperoxidase do?
utilized H2O2 and halide ions (Cl-) to produce hypochlorite, a highly toxic substance
what happens when some of the hypochlorite produced in oxygen dependent myeloperoxidase dependent intracellular killing breaks down spontaneously?
yields singlet oxygen
what are the toxic species produced in oxygen dependent myeloperoxidase dependent intracellular killing?
OCl- • singlet oxygen
activated macrophages (via PRR or INFγ) express high levels of what enzyme?
nitric oxide synthase
is NO+O2- more or less toxic?
which TNF is associated with increased expression of iNOS by macrophages?
how does TNFα affect production of Nitric Oxide?
TNF acts in an autocrine manner to induce the expression of the iNOS gene, resulting in the production of NO
what is the toxicity of NO in macrophages?
nitric oxide released is toxic and can kill microorganisms in the vicinity of the macrophage
what are the pro-inflammatory cytokines released by macrophages?
IL6 • TNF α • IL1β • CXCL8 • IL12
what are the systemic effects of IL6 released by macrophages?
1. fever • 2. induces acute phase protein production by hepatocytes
what are the local effects of TNFα released by macrophages?
activates vascular endothelium and increases vascular permeability, which leads to increased entry of complement and cells to tissues and increased fluid drainage into lymph nodes
what are the systemic effects of TNFα released by macrophages?
1. Fever • 2. Mobilization of metabolites • 3. Shock
what are the local effects of IL1β released by macrophages?
1. activates vascular endothelium • 2. activates lymphocytes • 3. local tissue destruction • 4. increases access of effector cells
what are the systemic effects of IL1β released by macrophages?
1. fever • 2. production of IL6
what are the local effects of CXCL8 released by macrophages?
chemotactic factor recruits neutrophils and basophils to site of infection
what are the local effects of IL12 released by macrophages?
activates NK cells
what was CXCL8 previously known as?
where does oxygen independent and dependent intracellular killing take place?
where does nitric-oxide dependent killing take place?
inside phagolysosome and cytosol
what does a defect in NADPH oxidase cause?
chronic granulomatous disease
what are the 8 steps of phagocytosis of a bacterium by a phagocyte?
1. chemotaxis • 2. adherence through PAMP recognition • 3. membrane activation through danger signal • 4. initiation of phagocytosis • 5. phagosome formation • 6. fusion • 7. killing and digestion • 8. release of degradation products
at what step of phagocytosis does tissue damage known as bystander damage take place?
release of degradation products
what does the complement system consist of?
several proteins, about 30, circulating in blood plasma, lymph and extracellular fluids
how are complement proteins designated?
C#...C1, C2, C3 • factor ALPHA... factor B, factor H
what produces complement proteins?
liver cells • monocytes • macrophages • gut epithelial cells
are complement proteins heat stable or heat labile?
how are complement proteins activated?
most of these are proenzymes, inactive until they are cleaved (complement activation)
what triggers complement activation?
microbial substances • immune complex (antigen + antibody)
how are cleavage products of complement activation designated?
split products are distinguished from the parent pro-enzyme by suffix lower case letters: • C3--> C3a + C3b
what happens to complement proteins when they are cleaved?
they become active enzymes, proteases, "convertase" that act on other complement components
In what fashion does complement activation take place?
in a sequential fashion
describe the cascade fashion in which complement activation takes place
many components of the system serve as the substrate of a prior component and then as an enzyme to activate a subsequent component
what does C'-fixation mean?
utilization of C' by antigen-antibody complexes
what are the 3 activation pathways of the complement system?
1. classic • 2. alternative • 3. lectin/mannan pathway
in which type of immunity are the 3 activation pathways of the complement system involved?
innate and adaptive immunity
what are the major functions of the 3 activation pathways of the complement system?
1. inflammation- vasodilation • 2. chemotaxis- attraction of cells of the immune system • 3. killing of pathogen cells by lysis • 4. opsonization- enhancing phagocytosis
what is an opsonin?
any molecule that targets an antigen for an immune response
what happens in the alternative pathway of complement activation?
pathogen surface creates local environment conducive to complement activation
which of the pathways of complement activation is first to act?
what happens in the lectin pathway of complement activation?
mannose binding lectin binds to pathogen surface
which of the pathways of complement activation is second to act?
what happens in the classical pathway of complement activation?
C-reactive protein or antibody binds to specific antigen on pathogen surface
which of the pathways of complement activation is the 3rd to act?
what happens in complement activation as a result of all 3 pathways of complement activation?
cleavage of C3 to C3a and C3b • C3b covalently bound to surface components of pathogen
what 3 things happens as a result of C3 cleavage and C3b binding to surface components of pathogen?
1. recruitment of inflammatory cells • 2. opsonization of pathogens, facilitating uptake and killing by phagocytes • 3. perforation of pathogen cell membranes • ...which collectively cause the death of the pathogen
what are the key steps in all pathways of complement activation?
1. initiation • 2. formation of the C3 convertase • 3. formation of the C5 convertase • 4. all pathways feed into terminal or membrane attack complex formation
is the alternative pathway part of the innate or adaptive immune response?
part of the innate immune response
what happens in the initiation of the alternative pathway of complement activation?
spontaneous cleavage of C3 at low rate in plasma: • - C3b gets inactivated in plasma, but: • --if it binds human cells, it is inactivated by complement regulator proteins produced by host cells. • -- if it binds to the surface of foreign microorganisms, it gets stabilized
what are examples of specific molecules on the surface of microorganism required for the alternative pathway of complement activation?
1. peptidoglycan • 2. teichoic acids • 3. lipolysaccharides
what triggers the alternative pathway of complement activation?
C3 hydrolysis directly on the surface of a pathogen
what does the alternative pathway of complement activation not rely on, that the other pathways do rely on?
where is C3 produced and cleaved in the alternative pathway of complement activation?
protein C3 is produced in the liver and is then cleaved into C3a and C3b by enzymes in the blood
what happens to C3a and C3b if there is no pathogen in the blood?
the C3a and C3b protein fragments will be deactivated
what happens in the alternative pathway if there is a nearby pathogen?
1. some of the C3b is bound to the plasma membrane of the pathogen. • 2. it will bind factor B • 3. this complex will be cleaved by factor D into Ba and the alternative pathway C3-convertase, Bb
what does C3bBb do?
The C3bBb complex, which is 'hooked' onto the surface of the pathogen, will act like a chain saw, catalyzing the hydrolysis of C3 in the blood to C3a and C3b, which positively affects the number of C3bBb hooked onto a pathogen.
what happens after hydrolysis of C3 in the alternative pathway of complement activation/
C3b complexes to become C3bBbC3b, which cleaves C5 into C5a and C5b.
C5a and C3a are known to trigger what?
mast cell degranulation
what is a membrane attack complex and how is it formed?
C5b, with C6, C7, C8, C9 (C5b6789) complex to form the MAC, which is inserted into the cell membrane, punches a hole, and initiates cell lysis.
which pathway provides another means of protection against certain pathogens before an antibody response is mounted?
the alternative pathway of C activation
what does a deficiency of C3 cause?
increased susceptibility to the organisms that activate the alternative pathway
which is the most primitive of the complement activation pathways?
what are the benefits of the alternative pathway of complement activation?
provides a means of non-specific resistance against infection without the participation of antibodies and hence provides a first line of defense against a number of infectious agents.
which protein has been extensively studied for its ability to activate the alternative pathway ?
cobra venom factor (CVF)
what happens when C3b associates with C3bBb?
C3BbCBb is formed
what is C3bBbCBb?
a C5 convertase
what kind of organisms activate the alternative pathway?
1. many Gram-negative bacteria (most significantly, Neisseria meningitidis and N. gonorrhoea) • 2. some Gram-positive • 3. certain viruses and parasites
In serum there is a low level of spontaneous hydrolysis of C3 to produce what?
Factor B binds to iC3 and becomes what?
susceptible to Factor D
what does factor D cleave factor B into?
what does the iC3Bb complex do?
acts as a convertase and cleaves C3 into C3a and C3b
What does factor B do once Cb is formed by cleavage of C3?
Factor B will bind to C3b and becomes susceptible to cleavage by factor D, resulting in a C3bBb complex.
what does the C3bBb complex generate?
more C3b, thus amplifying C3b production
what happens if C3 activation continues unchecked?
consumption of all C3 in the serum
what role does properdin play in alternative pathway control?
properdin stabilizes C3 convertase C3bBb
what are the roles of factors H and I in the control of the alternative pathway?
destabilization/destruction: • inactivation of C3b by factor H and I to give fragment iC3b
what does deficiency of factor H and I lead to?
depletion of C • fail to control infections
what role does DAF, MCP play in control of the alternative pathway
destabilization/destruction: • DAF and MCP disrupt C3 convertase C3bBb on a human cell surface
what does deficiency of DAF, MCP lead to?
destruction of self cells
What is DAF?
decay accelerating factor
What is MCP?
membrane co-factor protein
how do factor H and I avoid excessive usage and depletion of C3 from the plasma?
by inactivating C3b and preventing further cleavage of C3
when faced with bacterial infection, patients with factor H/I deficiency run out of C3 and fail to control infections, especially with WHICH TYPE of bacteria?
capsulated bacteria which require opsonization for elimination by phagocytic cells
what is the role of i3Cb?
deposited on surface of pathogens • serves as opsonin • facilitate phagocytosis by binding to CR3 and CR4 (complement receptors) on phagocytic cells.
what are the 2 main features of membrane attack complex formation (pathway)?
1. initiated by the formation of C5 convertase • 2. requires the presence of an accessible phospholipid membrane on the target cell on which to build the pore complex
what does formation of the c5 convertase trigger in the MAC formation (pathway)?
the association of a group of complement proteins which do not undergo cleavage but are active as intact proteins which build a transmembrane pore (MAC) in the target cell, resulting in leakage of cytoplasmic contents
what are examples of microbes resistant to MAC?
1. encapsulated bacteria • 2. gram positive bacteria • 3. un-enveloped viruses
what happens in the Membrane Attack (lytic) Pathway?
1. C5 convertase from the alternative (C3bBb3b) pathway cleaves C5 into C5a and C5b. • 2. C5a remains in the fluid phase and the C5b rapidly associates with C6 and C7 and inserts into the membrane. • 3. C8 binds, followed by several molecules of C9. • 4. The C9 molecules form a pore in the membrane through which the cellular contents leak and lysis occurs.
is membrane attack pathway lysis an enzymatic process?
no: • it is thought to be due to physical damage to the membrane
what is the complex consisting of C5bC6C7C8C9 referred to as?
the membrane attack complex
what are some of the potent biological activities of C5 generated in the lytic pathway?
1. it is the most potent anaphylotoxin • 2. it is a chemotactic factor for neutrophils and stimulates the respiratory burst in them • 3. it stimulates inflammatory cytokine production by macrophages
the activities of C5 generated in the lytic pathway are controlled by what?
carboxypeptidase B (C3-INA)
what intermediate of the lytic pathway can dissociate from the membrane and enter the fluid phase?
C5b67, the dissociation of which could cause damage to bystander cells
damage to bystander cells by C5b67 from the lytic pathway which has dissociated from the membrane is prevented by what?
Protein S (vitronectin): • Protein S binds to soluble C5b67 and prevents it from binding other cells
what binds to the C5b678 complex on human cells and prevents recruitment of C9 to form the pore?
what are the main features of the lectin (mannan) pathway?
1. part of the innate immune response • 2. nonspecific • 3. initiated when MBL binds to mannose or GlcNAc residues on microorganisms
what does initiation of the lectin (mannan) pathway activate?
MBL-associated serine proteases (MASPs) which split C4 and C2 to form C3 convertase
what happens after the initiation of the lectin (mannan) pathway creates the C3 convertase?
1. C3b is produced • 2. the C5 convertase (C4b, C2a, C3b) is formed and the MAC complex begins
To which other complement activation pathway is the Lectin pathway most similar?
the classical pathway
how is the Lectin pathway initiated?
by the binding of MBL to bacterial surfaces with mannose containing polysaccharides.
what are mannans?
mannose containing polysaccharides
binding of MBL to a pathogen results in what?
association of 2 serine proteases: • 1. MASP-1 • 2. MASP-2
what other proteins are MASP-1 and MASP-2 similar to?
C1r and C1s
what protein is MBL similar to?
formation of the MBL/MASP-1/MASP-2 trimolecular complex results in what?
the activation of the MASP's and subsequent cleavage of C4 into C4a and C4b
what happens to the C4a/b fragments formed by cleavage of C4 in the Lectin pathway?
1. the C4b fragment binds to the membrane • 2. C4a fragment is released into the microenvironment
in addition to cleaving C4 in the Lectin pathway, MASP's also cleave what?
C2 into C2a and C2b
what do C2a and C2b cleaved by the MASP's in the Lectin pathway do?
1. C2a binds to the membrane in association with C4b. • 2. C2b is released into the microenvironment
what is the function of the C4bC2a complex in the Lectin pathway?
it is a C3 convertase which cleaves C3 into C3a and C3b
what happens to C3a and C3b formed from cleavage by C4bC2a in the Lectin pathway?
1. C3b binds to the membrane in association with C4b and C2a. • 2. C3a is released into the microenvironment
what is the function of C4bC2aC3b complex in the Lectin pathway?
what is the end of the Lectin pathway?
generation of the C5 convertase
What are Ficolins?
a group of oligomeric lectins with subunits consisting of both collagen (Col)-like long thin stretches and fibrinogen (Fi)-like globular domains with lectin (Lin) activity usually specific for N-acetylglucosamine (GlcNAc)
what are Ficolins similar to?
ficolins are homologous to MBL and function via MASP in a similar way
what do ficolins do in non-vertebrates without an adaptive immune system?
ficolins are expanded and their binding specificities diversified to compensate for the lack of pathogen-specific recognition molecules
the biological activities and the regulatory proteins of the Lectin pathway are the same as those of what pathway?
the classical pathway
Is the classical pathway part of innate or adaptive immunity?
why is the classical pathway 'specific'?
due to the requirement of antibodies bound to the surface of particulate antigen
the classical pathway is activated by what?
the 'innate' classical pathway is activated by what?
C-reactive protein bound to pathogens
what complement protein does the classical pathway require?
what is C1 composed of?
C1q • C1r • C1s
what is the best activator of the classical pathway?
what are the weaker activators of the classical pathway?
some classes of bound IgG: • IgG3,1,2
What does the C1-complex consist of?
one molecule of C1q and two molecules of C1r and C1s
how is the classical pathway triggered?
by activation of the C1 complex
how is the C1-complex activated?
1. C1q'a binding to antibodies from classes M and G complexed with antigens • or • 2. binding of C1q to the surface of the pathogen
the binding of C1q to the antibodies or the surface of the pathogen leads to what?
1. conformational changes in C1q molecule, which leads to the activation of two C1r molecules. • 2. then C1r cleaves C1s
what does the C1-complex do after 2 C1r's cleave 2 C1s's in the classical pathway?
the complex now binds to and splits C2 and C4, producing C2a and C4b
the inhibition of C1r and C1s is controlled by what?
in the classical pathway, what molecules bind to form the C3 convertase?
C4b and C2a
which protein is larger, C2a or C2b?
what signals the end of the classical pathway?
production of the C3 convertase, but cleavage of C3 by this enzyme brings us to the start of the Alternative pathway
to what 2 things does C1 bind in the same way?
IgM and C-reactive protein
what are the 2 types of C3 convertase?
1. Lectin and Classical- C4bC2a • 2. Alternative- C3bBb
what are the types of C5 convertase?
1. Lectin and Classical- C2a4b3b • 2. Alternative- C3bBb3b
what does C4-BP inhibit?
What are the components of the Alternative pathway?
C3 • Factor B • Factor D • Properdin
what are the components of the Classical Pathway?
C1 • C4 • C2 • C3
what are the components of the Lectin pathway?
MBL • MASP-1 • MASP-2 • C4 • C2 • C3
is the Alternative pathway antibody initiated?
is the Classical Pathway Antibody initiated?
is the Lectin Pathway Antibody Initiated?
is the alternative pathway initiated by pathogen surfaces?
is the classical pathway initiated by pathogen surfaces?
Yes via antibody attachment or CRP
is the Lectin pathway initiated by pathogen surfaces?
is there anaphylotoxin generation in the alternative pathway?
is there anaphylotoxin generation in the classical pathway?
is there anaphylotoxin generation in the lectin pathway?
what is anaphylotoxin?
C3a • C5a
does the alternative pathway feed into the MAC?
does the classical pathway feed into the MAC?
does the Lectin pathway feed into the MAC?
what are the regulatory components of the alternative pathway?
Factor H • Factor I • DAF • CR1
what are the regulatory factors of the classical pathway?
C1-INH • C4-BP • Factor I
what are the regulatory components of the Lectin pathway?
C1-INH • C4-BP • Factor I
what type of pathogens do opsonization and MAC lysis target?
what are anaphylotoxins?
what type of anaphylotoxin is C4a?
a weak anaphylotoxin
what do anaphylotoxins do?
1. mediate degranulation of mast cells, basophils, eosinophils- release of biologically active mediator (eg histamine) • 2. promote smooth muscle contraction- increase vasodilation and vascular permeability (edema, low BP) • 3. mediate chemotaxis of leukocytes to sites of infection- activate macrophages and neutrophils • 4. promote platelet aggregation
what does C5a do to C' receptors?
increases expression of CR's on inflammatory cells (neutrophils, monocytes, macrophages, B cells)
describe the dose dependent action of anaphylotoxins
beneficial in low doses, cause anaphylaxis at high doses
What types of cells have C3a and C5a receptors?
1. smooth muscle cells • 2. Mast cells • 3. basophils • 4. eosinophils • 5. endothelial cells • 6. phagocytic cells • 7. platelets
what is the effect of anaphylotoxins increasing vascular permeability?
1. increased permeability allows increased fluid leakage from blood vessels and extravasation of complement and other plasma proteins at the site of infection • 2. Migration of monocytes and neutrophils from blood into tissue is increased
what is the binding action of the complement receptors on phagocytic cells?
CR1 binds to C3b • CR3 and CR4 binds to iC3b
what are the steps of opsonization and phagocytosis of bacteria?
1. complement activation leads to deposition of C3b on the bacterial cell surface • 2. CR1 on macrophage binds C3b on bacterium • 3. endocytosis of the bacterium by the macrophage • 4. macrophage membranes fuse, creating a membrane-bounded vesicle, the phagosome • 5. Lysosomes fuse with the phagosomes forming the phagolysosome
Describe step-wise the role of complement in clearing immune complexes from the circulation
1. circulating immune complexes become substrates for the activation of the classical pathway • 2. complement fragment C3b attaches to these immune complexes, mediating attachment of the complexes to RBCs via CR1. • 3. The RBC circulates the liver where CR1 acts as a cofactor for Factor I mediated cleavage of fragment C3b, forming the 2 products iC3b and C3f. • 4. iC3b is not bound by CR1, and so the RBC releases the immune complex, which is immediately bound by macrophages via CR3 or CR4. • 5. The macrophage ingests the immune complex
in the liver, CR1 acts as a cofactor for what cleavage reaction?
Factor I mediated cleavage of C3b
what are the products of factor I mediated cleavage of C3b in the liver?
iC3b • C3f
what happens to the complement level in the blood of patients with immune complex diseases?
patients with immune complex diseases will deplete their complement level in the blood
what is used in diagnosis of immune complex disease?
measurement of C2 and C4
What is the activity of C2b?
prokinin, accumulation of fluids
what is the effect of C2b?
what are the control factors for C2b?
what is the activity of C3a?
1. basophil and mast cell degranulation • 2. ennhanced vascular permeability • 3. enhanced smooth muscle contraction
what is the effect of C3a?
what are the control factors of C3a?
what is the activity of C3b?
opsonin, phagocyte activation
what is the effect of C3b?
what are the control factors of C3b?
Factors H and I
what is the activity of C4a?
1. Basophil and mast cell degranulation • 2. enhanced vascular permeability • 3. enhanced smooth muscle contraction
what is the effect of C4a?
anaphylaxis (least potent)
what are the control factors of C4a?
C4-BP and Factor I
what is the activity of C5a?
1. basophil and mast cell degranulation • 2. enhanced vascular permeability • 3. enhanced smooth muscle contraction • 4. chemotaxis • 5. stimulation of respiratory burst • 6. activation of phagocytes • 7. stimulation of inflammatory cytokines
what are the effects of C5a?
anaphylaxis (most potent) • inflammation
what are the anaphylactic activities of C5a?
1. basophil and mast cell degranulation • 2. enhanced vascular permeability • 3. enhanced smooth muscle contraction
what are the inflammatory activities of C5a?
4. chemotaxis • 5. stimulation of respiratory burst • 6. activation of phagocytes • 7. stimulation of inflammatory cytokines
what are the control factors of C5a?
what happens to prokinin?
cleaved by plasmin to yield kinin, which results in edema
Which has a higher plasma concentration, complement control proteins or complement proteins?
complement control proteins
what is an example of a control protein present on the membrane of self-cells preventing them from being targeted by complement?
CD59, which inhibits C9 polymerization during formation of the MAC
What syndromes/disease states are caused by deficiency of Factors B or D in the alternative pathway?
susceptibility to pyogenic bacterial infections