hCMB2004 Flashcards
1
Q
what are the sources of infection
A
- pathogens - organisms that cause disease
- bacteria
- viruses
- fungi
- parasites e.g. worms and protozoa
2
Q
what are the characteristics of an effective immune system
A
- be able to recognise and respond to any invading organism
- not over react to benign or self
- be able to direct different effector mechanisms against different pathogens
3
Q
what is specific/adaptive immunity
A
- is induced by exposure to a particular infection
- shows a high degree of specificity
- exhibits memory
4
Q
what are the features of specific immunity
A
- mediated by lymphocytes (B/T cells)
- clonal distributed receptors
- large repertoire:low frequency of cells specific for antigen
- response takes time to develop
- memory cells produced
5
Q
what is the clonal selection theory
A
- removal of potentially reactive immature lymphocytes by clonal deletions
- pool of mature naive lymphocytes
- proliferation and differentiation of activated specific lymphocytes to form a clone of effector cells
6
Q
what are the different types of lymphocyte receptors for antigen
A
- BCR expressed by B lymphocytes
- TCR expressed by T lymphocytes
7
Q
what are BCRs
A
- membrane form of Ig binds free antigen
- is subsequently secreted when B cell is activated now known as antibody
8
Q
what are TCRs
A
- membrane form only
- recognises peptide fragments of antigen bound to MHC expressed by APC
9
Q
what is the function of antibodies
A
- importance shown in cases where absent
- infection with encapsulated bacteria
- activation of complement
- activation of effect cells
10
Q
consequences of activation of complement
A
- opsonisation
- classical pathway activation and MAC
11
Q
consequences of activation of effector cells
A
- cells that express FcR (receptor that binds Fc region of antibody)
12
Q
what is the structure of antibodies
A
- paired variable regions (from heavy and light chains) from 2 identical antigen- binding sites
- constant regions are responsible for antibody structure and interacting with other molecules and cells of innate system –> antibody effector functions
13
Q
basic structure of antibodies
A
- immunologlobin
- basic 4-chain structure
- 2 identical heavy and light chains, held together by covalent/non-covalent bonds
- 2 types of L chain (gamma and kappa)
14
Q
what makes up antigen binding sites
A
- Vh
Vl
15
Q
what are the 5 classes of antibodies
A
- IgM
- D
- A
- G
- E
16
Q
what makes up the different isotopes
A
- different isotopes are determined by the heavy chain
- isotopes differ in their structure and functions
17
Q
what are antibody domains
A
- analysis of amino acid sequences of H and L chains reveals homology regions
- L chain - 2 domains
- H chain - 4 or 5 domains
- each domain comprises two beta sheets
- linked by a disulphide bridge
18
Q
what’s included in the immunoglobulin superfamily
A
- TCR
- MHC class I and II
- CD4, CD8, CD80, CD96, CTLA-4, KIR, IL-6R
19
Q
how to antigens interact with antibodies
A
- hypervariable regions (3 in Vh and Vl
- HV1-3
- 6 hypervariable loops - antigen binding site
- complementary-determining regions
- antigen binds to aa in CDRs
- size/shape of antigen affects binding
20
Q
how are antigens recognised
A
- epitopes recognised by antibodies may be continuous or conformations
- antibody and antigen form non-covalent interactions
- CDRs present in antibody V regions determine the specificity and the affinity of an antibody for antigen
21
Q
what are the functions of TCR
A
- doesn’t bind free antigen
- binds/recognises processed antigen
- presented in the cleft/binding groove of MHC class I or class II molecules
22
Q
what are MHCs
A
- major histocompatibility complex
- different expression patterns
- present peptides for different sources
- first identified fur to role in transplant rejection
23
Q
what are MHC class i
A
- expressed on all nucleated cells
- heterodimer - alpha and beta2 chains
24
Q
what are the 3 different MHC class I molecules
A
- HLA-A
- HLA-B
- HLA-C
25
what forms the peptide binding site in MHC class i
- the alpha 1 and alpha 2 domains forms to form beta-sheets structure
26
key points of MHC class II
- expression limited to APC
- heterodimers, alpha and beta chains similar size and both transmembrane
27
what are the 3 different types of MHC class ii
- HLA-DP
- HLA-DQ
- HLA-DR
28
what forms peptide binding sites in MHC class II
- polymorphic alpha 1 and beta 1 domains
29
what makes up H chains in TCR beta
- V region encoded by 3 gene segments
- V,D J (V is the biggest)
30
what makes up L chain in TCR alpha
- V regions encoded by 2 gene segments - V and J
31
what causes the rearrangement of Ig genes
- in B cells the DNA containing the Ig gene segments is deliberately broken and the gene segments are rearranged to form function Ig genes
- non-homologous end joining recombination
- each individual B cell will perform both the breakage and rearrangement randomly
32
how are functional immunoglobulin genes produced
- after DNA breaks, a single V and a single J gene segment are joined together to encode the v region of the light chain
- this process is random
- a random V, D and a J gene segment are joined together in single B cell to encode the V region of the heavy chains
33
what is the specific order of Ig rearrangement in B cell development
- H chain gene segments rearrange (D-J then V-DJ)
greater variability of H chains
- then the light chain gene segments rearrange (kappa first)
- if kappa rearrangement is unsuccessful, then gamma gene segments rearrange
34
which chromosome are the different loci present
- H chain locus - chromosome 14
- kappa chain locus - chromosome 2
- lambda chain locus - chromosome 22
35
what are the stages in the recombination process
- Ig gene segment rearrangement is guided by special sequences flanking each of the V,D and J gene segments = recombination signal sequences
- rearrangement involves a complex of enzymes - V(D)J recombinase
- recombination activating gene
36
what are recombination activating genes
- RAG1 and RAG2 genes encode lymphoid specific components of the recombinase
- mutations in RAG genes results in immunodeficiency
37
what is allelic exclusion
- in each individual B cell, only one rearranged H chain gene from one chromosome is expressed
- only one rearranged L chain from one chromosome is expressed by each individual B cells
- light chain isotope exclusion
- these mechanisms ensure that each individual B cell produces just one randomly generated BCR that is different from the BCR made but every B cell
38
what is light chain isotope exclusion
- each B cell expresses either a rearranged kappa an lambda
- light chain; never both
39
what is combinatorial diversity
- different V,D, J segments recombine to produce different seuqneces
40
what are the mechanisms for generation of antibody diversity
- there are multiple gene segments for each chain
- combinatorial diversity
- combinations of heavy and light chains
- junctional diversity increases further
- somatic hypermutations
41
how is junctional diversity increased further
- imprecise joining (small differences in sequences where V-D and D-J segments join)
- N regions (random addition of nucleotides at junctions of V-D and D-J by terminal transferase
42
what are somatic hypermutations
- mutation frequency in antibody V genes is orders of magnitude higher than seen in all other areas of the genome
- SHM occurs in germinal centres as B cells recognises antigen and proliferate
43
how do SHM occur
- performed by the enzymes, activation-induced deaminase
- AID acts on DNA to de-aminate cytosine to uracil
- uracil is then recognised by error prone DNA repair pathways leading to mutations
44
membrane vs secreted antibody
- following Ag recognition as each B cell differentiates, it will start to secrete its unique BCR as an antibodd
- the secreted form made by each B cell has an alternative constant region that lacks transmembrane regions. as the original re-arranged VDJ regions are not altered, the secreted antibody has the same antigen specificity as the membrane BCR
- the membrane and secreted forms are produced by alternative RNA processing
45
what is class switching
- at the heavy chain locus, the Cmuw segment is physically closest to the V, D and J gene segments and so IgM is the first class expressed by each developing b cell
- Cdelrta is next to Cmuw - hence IgD can be co-expressed with IgM by differential processing of the RNA from the two C region genes
46
what is required for switching to other classes
- requires further DNA recombination - guided by switch regions
- this process also involves the enzyme AID pathogen --> cytokine --> switch
47
why does class switching occur
- as a result of the cytokine that may be present in this environment
48
where are T cells developed
- thymus
49
TCR VS BCR
- TCR is never secreted
- no SHM occurs in TCR genes
- TCR generation is very similar to the DNA rearrangement process seen in BCR generation
50
where are MHC class I expressed
- all nucleated cells
51
where are MHC class ii expressed
- on particular cell types e.g. B cells, macrophages, dendritic cells (antigen presenting cells)
52
how are MHC molecules polymorphic
- many alleles
- a single individual will have up to 12 different MHC molecules (if there are heterozygous for all 6 MHC loci
53
what is co-dominant expression of MHC molecules
- 3 MHC class I molecules
- of heterozygous at each loci, one person can express six different class I molecules
similarly for class II
- polymorphism and polygeny
54
what is the importance of high levels of MHC polymorphism
- allows the binding of a vast range of peptides that can be presented to T cells, provides a clear evolutionary advantage to the population as can respond to almost unlimited number of different pathogens
55
what are the downsides of high polymorphic MHC
- increases risk of immune mediated disease e.g. autoimmune diseases
- also reduced pool of available donor organs for transplantation - as MHC alleles should match for best outcome
56
how do peptides end up on the surface of cells bound to MHC molecules
- peptides derived from protein antigens synthesised inside a cell are usually presented by class I MHC molecules
- peptides derived from protein antigen taken up from the outside of the cell are usually presented by class II MHC molecules
57
how are antigens presented by MHC class I molecules
- intracellular antigen
- antigen processing to peptide in proteasome
- peptide transport into endoplasmic reticulum
peptide binding by MHC class I
- MHC class I present peptide at cell surface
58
how are antigens processed by MHC class I
- antigen synthesised in cytoplasm
- protein cleaved to peptides by proteasome
- peptides transported to endoplasmic reticulum by TAP transporters
59
what are proteasome
- proteasome functions in all cells - cytoplasmic protein turnover
- proteasome in cells receiving inflammatory cytokines signals are modified to produce altered peptides
- TAP is a component of a multi-protein assembly, the peptide loading complex - also induces tapas in and calreticulin
60
function of proteasome
- cytosolic proteins are degraded to peptide fragments by the proteasome a large multicatalytic proteases
61
how are antigens processed by MHC class II molecules
- antigen endocytosed into intracellular vesicles inside the cell
- protein cleaved to peptides by acid proteases in vesicles
- vesicles fuse with vesicles containing MHC class II molecules
- peptides bind MHC class II molecules
- MHC II then transported inside vesicles to cell surface
62
how is CLIP created
- invariant chain forms a complex with MHC class II molecules, blocking the binding of peptides and misfiled proteins
- II is cleaved in an acidified endoscope, leaving a short peptide fragment, CLIP, still bound to MHC class II
- endocytosed antigens are degraded to peptides in endoscopes, but the CLIP peptide blocks the binding of peptides to MHC class II molecules
- HLA-DM binds to the MHC class II molecules, releasing CLIP and allowing other peptides to bind. the MHC class II molecule then travels to the cell surface
63
what happens to CLIP at the cell surface
- MHC class II molecules bind to invariant chain in the ER
- this prevents peptides binding in the groove
- in endocytic pathway lysosomal enzymes degrade this leaving CLIP peptide associated with binding groove
- peptides from antigen displace CLIP when they bind
- HLA-DM a class II like molecule, is required for loading of peptides into the groove
64
what happens to MHC class I and II in normal healthy cells
- MHC I and II will bind and present peptides from self protein
65
what accessory molecules are involved in antigen processing and presentation
- TAP and LMP ( class I pathway)
- HLA-DM (class II pathway)
66
what are antigen presenting cells
- specialised cell types that express MHC class II molecules
- take up and present extracellular Ag to activate helper CD4+ T cells
- e.g. macrophages, dendritic cells, B cells
67
what happens to viruses in MHC class I
- as all nucleated cells express MHC class I molecules, any cell infected by a virus can present viral peptides on MHC class I molecules and be recognised and killed by cytotoxic CD8+ T cells
68
how are B cells developed
- develop from haematopoietic stem cells in bone marrow that express PAX5 transcription factor
- involves rearrangement and expression og ig genes
- expression of lymphocyte, and the B cell specific markers e.g. CD45 then CD19
- removal of self-reactive cells
69
how doB cell precurors rearrange its immunoglobulin genes
- generation of B cell receptors in the bone marrow
- adhesion molecules, close relationship between storm cells, negative selection of those that are auto reactive
70
how are immature B cells produced
- H chain genes rearrange first moves to cell surface with Igalpha and Igbeta and expressed with surrogate light chain
- then light chains rearrange, and displace V preB and lambda5 chains --> IgM BCR
- immature B cells
71
how are pre B cell receptors formed
- early pro B cell - Vh to DJh rearrangements occur
- large pre B cell - stop heavy chain gene rearrangement
- immature B cells - stop light chain gene rearrangement
- mature B cells
72
how are Ig genes rearranged during B cell development
- stem cell
- early pro B cell
- late pro B cell
- large pre B cell
- small pre b cell
- immature B cell
- mature B cells
73
what is the function of pre-BCR
- delivers signal to pre B cell that H chain looks functional
74
how is a signal from pre-BCR produced
- turns off RAG 1 RAG2 genes
- cell division
- surrogate light chain expression stops
- RAG1 and RAG2 turned on again
- L chain rearrangement starts
- RAG genes needed for gene rearrangement
75
what rearrangement happens in early pro B cells
- H chain gene rearrangement
- D-J rearrangements on both chromosomes
76
what rearrangements happen on late pro B cell
- H chain gene rearrangement
- V-DJ rearrangement on first chromosome
- V-DJ rearranagement on second chromosome
- cell loss
77
what rearrangements happen in immature B cells
- rearranagement ceases
- cell expresses muw:kappa
- cell expresses muw:lambda
78
which type of light chain will B cells express more of
- as kappa light chain genes rearrange before lambda genes, more B cells will express kappa and lambda light chains
79
how are repeated rearrangements possible at the light chain loci
- importance of signalling of pre B cell BTK involved, if not present GT no mature B cells being produced
80
how are immature B cells tolerant
- bind multivalent self antigen undergo clonal deletion or receptor editing
- bind soluble self-antigen --> cell becomes unresponsive
- binding of self-antigen by immature B cells leads to death or inactivation
81
how are T cells developed
- originate from bone marrow stem cells
- rearrange receptor genes (once in thymus)
- express pre T receptor
- elimination of self-reactive T cells by negative selection
82
how are alpha/beta T cells developed
- in the thymocytes:
- rearrange TCR genes and express TCR
- acquire other markers e.g CD3, CD4, CD8
- undergo positive and negative selection
83
what is the thymus
- bi-lobed organ in anterior mediastinum
- each lobe divided into many lobules
- each lobule has outer cortex and inner medulla
- cells e.g. lymphoid cells, epithelial cells, macrophages and dendritic cells
84
how do T cells mature in the thymus
- pro-thymocytes enter cortex via blood vessels from bone marrow
- firstly, they rearranged TCR beta genes
- expressed along with pre T cell receptors
- cells proliferate and then re-arrange TCR alpha genes
85
what is the TCR complex
- TCR expression requires the CD3 complex
- CD3 transmits signal to T cell nucleus following TCR recognition of p/MHC
86
what are lambda-delta TCR
- lambda-delta T cells do not express CD4 or CD8 markers
- recognise different antigens from alpha-beta T cells
87
importance of alpha/beta TCRs
- recognise self MHC and peptide from foreign ag
- recognise self MHC and peptide from self ag
- not able to recognise self MHC
88
what is positive selection of T cells
- positive selection of cells which recognise self MHC
- positive selection of alpha:beta T cells by cortical epithelial cells in the thymus
89
what is negative selection of T cels
- TCR binding to MHC with high affinity causes T cell to die apoptosis
- negative selection of alpha:beta T cells by dendritic cells, macrophages, and other cells in the thymus
90
why is TCR affinity for p/MHC the basis for selection
- all T cells recognising self MHC/self peptide are positively selected
- those with the highest affinity TCR are then negatively selected
91
how are the different types of cells related to MHC
- a die due to insufficient affinity for self MHC
- b and c are positively selected, but b are then negatively selected due to high affinity for self MHC
- c intermediate affinity and survive
92
what happens to cells that survive thymus selection
- express TCR capable of binding self mic
- are depleted of self-reactive cells
- exit the thymus as mature, single positive T cells
93
what type of T cells do naive T cells turn into
- cytotoxic effector T cells (CD8+) - kill infected cells
- helper effector T cells (CD4+) - secrete cytokines
94
what happens to naive T cells
- must encounter antigens for survival
- enter lymph node from blood via high endothelial venules
- move into T cell are which is rich in dendritic cells and macrophages
- T cells enter lymph node cortex from the blood via high endothelial venues
95
what are cell adhesion molecules
- molecules expressed on surface of T cells, bind ligands expressed/released by other cells
- once close to other cells different molecular sets of CAMs mediate cell/cell interactions
96
how do T cells contact APC
- using CAMs
- T cells initially bind APC through low affinity LFA-1:ICAM1 interaction
- subsequent binding of T cell receptors signals LFA-1
- conformation change in LFA1 increases affinity and prolongs cell-cell contact
97
what are the 3 types of signals APCs deliver to naive T cells
- activation
- survival
- differentiation
98
how is co-stimulation negative feedback
- once activated T cells now proliferate and express ICOS and CTLA-4
99
what is the role of ICOS
- binds ICOSL on APC to induce cytokine secretion by T cells
100
what is the role of CTLA-4
- is highly related to CD28, and shows stronger binding to B7.1/2 than CD28
- CD28 delivers inhibitor signals to activated T cells
101
what is the importance of CTLA-4
- CTLA-4 mutations associated with several autoimmune diseases
102
what is the function of signal 3 (cytokines)
- dictate the differentiation of activated CD4 cells into different sub-sets of effector cells
- delivered by antigen presenting cells
- TGF beta --> Treg cells
- IL-6 --> TFH cells
- TGF beta IL-6 --> Th17 cells
- IL12 IFN-lambda --> TH1 cells
- IL4 --> Th2 cells
103
what are the two types of DC
- myeloid
- plasmacytoid
104
what is the function of Myeloid
- kep APC that initiate T cell responses
- bone marrow derived
- immature form found in epithelia
- do not express co-stimulatory molecules *B7) until activated
- released upon danger signal
105
what is the function of DC
- mature DC are found in T cell areas of lymphoid tissues
- DC MHC I and ii will be loaded with peptides from pathogens they encountered in peripheral tissues
- their levels of co-stimulatory molecules will be very high
- they will express high levels of adhesion molecules
- efficient activators of naive T cells
106
how do DC activate naive T cells
- immature dendritic cells in peripheral tissues encounter pathogens and are activated by PAMPs
- TLR signalling induces CCR7 and enhances processing of pathogen derived antigen
- CCR7 directs migration into lymphoid tissues and augments expression of co-stimulatory molecules and MHC molecules
- mature dendritic cell in T cell some primes naive T cells
107
what is cross presentation
- some specialised DC take up and process exogenous antigen and present it via MHC I molecules
- this allows these DC to activate naive CD8+ T cells. this means these CD8 effector cells can kill infected cells that are not APC so not expressing co stimulatory
108
what are macrophages
- function as killers of pathogens but also important APC for extracellular pathogens
- highly phagocytic
- express MHC class II and B7 which increases following T cell help
- once activated by T cells secrete many inflammatory cytokines
109
how can B cells act as antigen specific APC
- antigen binding to BCR up regulates B7
- specific antigen efficiently internalised by receptor mediated endocytosis
110
what is the role of interleukin 2
- IL2 is a potent autocrine T cell growth factor
- IL2 binding to IL-2R on activated T cells results in T cell proliferation
111
how are CD8+ T cells activated
- requires high levels of co-stimulator activity
- CD8+ T cells can be activated directly by infected or cross presenting APCa
112
what is the role of a progenitor
- gives rise to a large number of lymphocytes, each with a different specificity
113
how do B cells become activated
- mature B cells bound to foreign antigen is activated
- activated B cells give rise to plasma cells and memory cells
114
what is the molecular basis of ag/BCR signal 1
- BCR-associated polypeptides involved in signalling
- crosslinking BCR activated intracellular kinase
115
how can signal 1 be increased
- if antigen has activated complement cascade
- lots of c3b
- complement receptor 2 on B cell surface (cd21)
- CR2/CD19/CD81 form the BCR co-receptor complex
- augments the signal
116
what provides signal 2
- antigen itself
- extensive cross linking of BCR
117
what is the role of thymus independent antigen 1
- TI-1 Ag bind to other receptors on all B cells providing signal 2
- in high concentrations the antigens acts as polyclonal activators for B cells
- the 2 signal lead to B cell activation proliferation and antibody secretion
118
what is the role of TI-2 Ag
- contain repeated epitopes
- will therefore cross link many BCR molecules on same B cell surface
- TI-2 antigens alone can signal B cells to produce IgM antibody
- activated dendritic cells release a cytokine, BAFF, that augments production of antibody against TI2 antigens and induce class switching
119
what are thymus dependent antigens
- antibodies to TD Ag, requires presence of CD4+ T cells
- antibody responses seen to TD Ag are much better than those of TI Ag
120
how do B cells process and present Ag
- CD4+ T cells --> receive signal 2
- via CD40/CD40-L interaction
- cytokines secreted by T cells (help B cell to class switch)
121
how are thymus independent and thymus dependent antigens converted
- B cell binds bacterial polysaccharide epitopes linked to tetanus toxoid protein
- antigen is internalised and processed
- peptides from protein component are present to the T cell
- activated B cell produces antibody against polysaccharide antigen on the surface of the bacterium
- way of improving the efficiency of a vaccine against pathogens that have T1 antigens
122
what is an example of a conjugate vaccine
- haemophilus influenza type B
- TI Ag is coupled to a protein such as tetanus toxoid which then converts it to a TD Ag
123
what is the role of CD40
- CD40 signal also induces activation induced deaminase which is required for class switching and somatic hypermutation
124
how are B cells activated with TD Ag
- conjugates of B lymphoblasts and T cells mode to primary follicles
- form germline centres within a B cell follicle in secondary lymphoid tissues
- B cells divide rapidly to become centroblasts and undergo SHM and switching
- differentiate into non-dividing centrocytes
125
what happens to B cells in GC
- differentiate into plasma cells
- form long lived memory cells
- die within lymphoid tissues
126
where are GC found
- in follicular dendritic cells
127
what is the role of CD40
- CD40 signal via CD40 L-expressed on Tfh (protects centrocytes from apoptosis
- induces isotope switching (different cytokines induce different isotopes to be produced
128
what are the different isotypes
- polysaccharides - IgM
- proteins - IgG1 and IgG3
- IgA - antigens at mucosal surface
- IgE
- IL4 important for IgE switch
129
why do we need immunological tolerance
- random generation of repertoire of BCR and TCR
- many self-reactive specificities will be produced
130
what are the consequences of random TCR gene rearrangement
- fail to recognise self MHC
- recognise self MHC + peptide generated from Ag present in the thymus
- recognise self MHC and any other peptide not present in the thymus
131
what are AIRE
- autoimmune regulator proteins
- transcription factor
- allows the expression of many tissue-specific Ag in the thymus
132
what is Ig gene rearrangement
- re-arrange another light chain
133
what are the mechanisms of tolerance
- anergy - leaving bone marrow as unresponsive
- immunological ignorance - insufficient levels to activate T cells
- privileged site - suppressive cytokines
- many B cell responses are T cell dependent - no antibody response
134
what is the mechanism of tolerance regulatory B cells
- B cells recently described that secrete IL-10 are crucial in preventing autoimmunity
135
why is it important to regulate immune responses
- to ensure responses continue only for as long as they are needed
- to minimize collateral damage
- to ensure responses are qualitatively appropriate
136
what are the different effector T cells
- Th1
- Th2
- Th18
- Treg/Breg
- Tfh
137
what is the role of Th1
activation of macrophages, NK cells and cytotoxic T cells
express CD40L
138
what is the role of Th2
promote responses mediated by eosinophils and mast cells; role in antibody responses, especially IgE
secrete IL-4
139
what is the role of Th17
promote responses against fungi
secrete IL-17
140
what is the role of treg/breg
suppress unwanted responses
contain CD4+ CD25+ CD8+
Secrete IL10 and TGF beta
141
what is the role of Tfh
specialised Th found in GC to help B cells
142
what is inhibited by Th1 cytokines
- development of Th2 and Th17
143
what is inhibited by Th2
- development of Th1 and Th17
144
what is inhibited by Th17
- development of Treg
145
what is inhibited by Treg
- Th1, Th2, Th17
146
what is the importance of polarised responses
- ensures correct responses for different types of pathogens
- can go wrong may lead to allergy (excessive Th2)
- control of auto reactivity/pregnancy
147
what are the organisms that may cause disease
- bacteria e.g. salmonella, streptococci
- viruses e.g. HIV flu
- fungi e.g. candida, pneumocystis carinii
- parasites e.g. schistosome, trypanosome
148
what do the different effector mechanisms depend on
- type of pathogen
- localisation
- challenge
- stage on infection
149
what are the two types of host defence mechanisms
- innate defence mechanisms
- acquire/adaptive defence mechanisms
150
two examples of gram positive bacteria
- staphylococcus aureus
- streptococcus app.
151
what are the examples of gram negative bacteria
- campylobacter
- salmonella
- shigella
- haemophilus neisseria
152
what are the features of the gram positive cell wall
- thick layer of peptidoglycan cell wall
153
what are the features of the gram negative cell wall
- much thinner
- has an outer membrane containing LPS
154
how do the components of cell walls induce innate responses
- bind to toll-like receptors on macrophages
- 10 TLR in humans - recognise distinct patterns on microbes
- nucleotide binding oligomerisation domains
155
what can binding of toll like receptor induce
- promote inflammation
- promote dendritic cell maturation
- influence differentiation of T cells
- activate B cells
156
what is the role of antibodies in bacterial infections
- opsonisation
- complement activation
- bind to and neutralise toxins
- bind to surface structures to prevent mucosal adherence
157
what are the stages of complement activation
- promote inflammation via c3a, c5a
- opsonise by binding c3b receptor on phagocytes
- lysis of gram negative organisms
158
what is needed for protection against bacterial infection
- antibodies important in protecting against extracellular pathoegns
- T cell effector mechansims protect against intracellular organisms
159
what are the 2 possible outcomes of leprosy
- tuberculoid - strong Th1 response
- lepromatous - strong Th2 and antibody response
160
what are type 1interferons
- synthesis of IFNalpha and IFNbeta induces in virus-infected cells
161
Which type of bacterial infections can the MAC be particularly useful in killing the
pathogen
- gram negative bacteria can be killed by complement lysis
162
what are type 2 interferons
- IFNlambda secreted by activated T cells and NK cells
- inhibits Th2 response and promotes Th1
163
what are natural killer cells
- types of innate lymphoid cells
- larger granular lymphocytes
- can recognise stressed cells in absence of Igs and MHC
164
what are the two types of NK cell receptors
- activating receptors - recognise carbohydrate ligands, trigger killing
- inhibitory receptors - recognises MHC class I molecules
165
what are the two mechanisms cytotoxic T cells use to kill cells
- secretion of cytotoxic granules
- FAS ligand on T cells interact with Fas on target
166
what are CTLs
- CTL recognises and binds virus infected cells
- CTL programs targets for death including DNA fragmentation
- CTL migrates a new target
167
what is the role of IFNlambda
- inhibits viral replication
- up regulates MHC class I and II expression and antigen presentation
- increases macrophage phagocytosis of dead cells
- promotes NK cell killing activity
168
what is the role of antibodies in specific immunity
- neutralise free virus
- opsonise to increase phagocytosis
- activate complement leading to lysis
169
stages of HIV infection
- attacks specific immune systems
- target CD4 T cell, macrophages and dendritic cells
- progressive development of AIDS leads to opportunistic infections
170
what is the role of antibodies in acquired immunity
- antibody and cell mediated immunity in influenza
- infection induces antibody and cytotoxic T cell response
- antibody recognises haemagglutinin and neuraminidase
- high levels of CTL activity correlates within reduced viral shedding
171
importance of CTLs in HIV
- patients with higher levels of CTL activity show slower disease progression
- virus mutations that escape CTL recognition may lead to progression of AID
172
what is the immune response
- dampens anti viral type 1 interferon --> aids viral replication
- viral proteins can inhibit RIG1
- viral proteins can stimulate NFkB activation --> pro inflammatory
- antibodies protective and role of cytotoxic T cells
173
what are the mechanisms used by antibodies
- opsonisation
- complement lysis
- antibody dependent cell mediated cytotoxicity
174
effector mechanisms induced by malaria
- sporozoite and merozite may be susceptible to antibody
- antibody may also kill infected red blood cells
- cytotoxic T cells active against liver cells
175
what are evasion mechanisms
- concealment of antigens
- antigenic variability
- immunosuppression
- interference with effector mechanisms
176
what is concealment of antigens
- some viruses inhibit antigen presentation by MHC class I
- privileged sites
- uptake of host molecules
177
what is antigenic variability
- large number of antigenic types
- mutations
- recombination
- gene switching
178
what is streptococcus pneumonia
- leading cause of serious bacterial infections
- gram positive
179
what are the two streptococcus pneumoniae vaccine
- pneumovax
- Prevnar 13
180
what is the correlation between antigenic variability and the influenza virus
- the influenza virus can undergo antigenic drift and antigenic shift
181
what is the relation between trypanosome and gene switching
- changes in the major surface antigen of the trypanosome, brought about by genetic rearrangement
- variant specific glycoprotein
182
what causes immunosuppression
- infection of immune cells
- induction of regulatory T cells
183
what biomarkers do regulatory T cells express
CD4 and CD25 on the surface and foxp3
184
how do regulatory T cells leishmania induce immunosuppression
- can hide and survive in macrophages
- can increase expression of Treg cells
- decrease immune response
185
what are dendritic cells
- antigen presenting cells
- act as messengers between the innate and adaptive immune system
186
what are the interference with effector mechanisms
- molecules interfering with antibody function
- molecules interfering with complement
- molecules binding cytokines
- subvert responses by producing molecules with cytokine activity
- inhibition of phagocytic killing
187
what are the pathological consequences of immune responses
- innate - LPS induce macrophage cytokine secretion
- specific - antibodies and/or T cell reactions may contribute to pathology
- microbes play a role in initiating autoimmune responses
188
what are the requirements of an effective vaccine
- safe
- high level of protection
- long lasting protection
- right type of response
- low cost
- stable
- easy to administer
- minimal side effects
189
what are the 5 main types of vaccines
- inactivated organisms
- attenuated organisms
- subunit vaccines
- toxoid
- conjugate something with low antigenic property covalently bound to something with high
190
what are adjuvants
- a substance administered with an antigen to promote the immune response
- pure antigens often elicit weak immune responses
- adjuvants enhance immune responses
191
what are the various ways adjuvants act
- activate dendritic cells via TLRs or NLRs
- cause release of endogenous danger signals
- promote antigen uptake by dendritic cells
- stimulate release of chemokine/cytokines
- promote cross-presentation of exogenous antigens by class I
192
what are the adjuvants used in clinical practice
- MF59
- AS03
- AS04
193
what is an antiserum
- contains antibodies that bind the antigen, along with other soluble blood components but doesn't contain cells or clotting proteins
194
how do we purify different antibodies
- gel filtration chromatography
- affinity chromatography
195
what are the limitations of using antisera
- once the antiserum has been used, then another individual will need immunising and the antibodies generated with never be exactly the same
196
what are the uses of antibodies
- antiserum
- purified polyclonal antibodies
- generation of monoclonal antibody producing hybridoma
197
how are secondary antibodies produced
- collect mouse sera
- contains many different mouse antibodies
- purify mouse antibodies
- collect rat anti-mouse antiserum
- purify ran anti-mouse polyclonal antibodies
198
what are the uses of antibodies
- in research
- in diagnostic
199
what is enzyme linked immunosorbent assay
- detection of linear/non linear epitopes
- very sensitive - detect the presence of a specific biological material
- very reproducible
200
what are the the different classes of ELISA
- direct ELISA
- indirect ELISA
- sandwich ELISA
201
what are the steps of direct ELISA
- antigen added to plastic plate
- labelled antibody added
- substrate added
- measure substrate conversion
202
what are the steps of indirect ELISA
- antigen added to plastic plate
- unlabelled primary antibody added
- labelled secondary added
- substrate added
- measure substrate enzyme label
203
what are the steps of sandwich ELISA
- unlabelled antibody added to plate
- sample added
- add labelled secondary
- add substrate
- measure substrate conversion
204
what can antibodies identify
- the presence of a protein
- the location of a protein
- characterising cells based on the presence of a marker protein
205
what is flow cytometry
- measures how single cells in a population affect a laser beam as they pass through it
206
