Flashcards in Adaptive immunology Deck (33):
what is the clonal selection theory?
Ab-producing precursor B-cells are produce and make (IgM) Abs even before Ag is present; the B cells express Ab on their surface; all Abs presented are of the same class and have the same specificity; when the Ag binds to the Ab, the B cell secretes Abs; also, B cells multiply once they have been activated (by Ag binding to Ab) so that enough Abs can be made; the B cells that differentiate to secrete Abs are known as plasma cells
describe the mechanisms that generate Ab diversity without the presence of Ag
Combinatorial--variations of segments of genes (VDJ for heavy), VJ (for light) are rearranged in the variable chains; RAG binds to RSS, cuts segment out;
Junctional--inserts nt where segments join up-->frameshift mutation; one of the strongest ways to generate diversity
what is allelic exclusion?
we contain two copies of each chromosome, one from mother and one from father; after one chromosome has successfully undergone VDJ/VJ recombination, the other chromosome is shut off (excluded from contributing to Abs in B cell)
what does it mean if the adaptive system is somatically generated?
it means there are unique cells which contain unique DNA that contain these hypervariable regions
what is CSR? why is it important?
class-switch recombination; a CD4+ and T cell dependent process where the constant chain region of the chromosome is altered such that an M/G/E etc class of Ab is created; also requires the AID enzyme; important because class switching happens after the Ag is present, and IgM Abs are initially produced-->but they do not bind tightly to Ag, so the already-made Abs need to be switched to IgG
what is SHM?
somatic hypermutation; deamination of cytidine to uracil via activation-induced cytidine deaminase; occurs in the variable region of the Ab; does not change specificity, but tweaks affinity;
Affinity maturation: the B cell will only survive if SHM increases the affinity of the antibody of this B cell. Since SHM inserts random mutations, affinity might decrease (or the specificity might change) and the B cell will die
how does a B cell control how to display or secrete an Ab?
mRNA splicing; if the mRNA is spliced such that an exon exists at the end, it will signal to the B cell that it should be membrane bound-->so it will be displayed on the B cell; no exon-->no signal, is secreted
what is antiserum?
a serum that contain antibodies specific for a particular antigen (ex: H1N1 antiserum)
what is serology?
the study of Abs present in the blood
what are mabs?
Monoclonal antibodies: antibodies derived from one clone of B cells identical antibodies specific for the same epitope
Used for therapygood, because it contains only one epitope
what are polyclonal Abs?
Polyclonal antibodies: from multiple clones of B cells
what is the definition of antigenic?
can be recognized by the immune system
what is immunogenic?
can induce the immune response
On its own
describe hapten-carrier immunology;
hapten is a small molecule that cannot elicit an immune response; it must be coupled to a carrier; then, when coupled to a carrier, B cells can make Abs against both the hapten and carrier; the hapten alone cannot make stimulate the B cell to make Abs; when the T helper cells will help B cells with immune response and will bind to the carrier; the carrier acts as a bridge between B cell/hapten and T cells??
what acts as a bridge between the Fab fragment and FcRs (the immune system)?
what are the functions of Abs?
2. opsonization (phagocytes contain FcR receptors)
3. compliment activation
4. ADCC (NK cells)
5. activation of mast cells and basophils
what are the differences between bound and unbounds Abs?
change in conf shape
aggregation of bound Abs
The first class of antibody to be produced in an immune response
Has low affinity for the antigen
Very efficient at activating complement
Activate mast cells and basophils by binding to FcR’s
Very important in allergies and parasitic infections
Various functions depending on the type
More affinity for the antigen
Can act as opsonins
IgG1, 2, and 3 can activate complement
IgG4 is different, you will learn about it in future lectures (can counteract the effects of other antibodies)
Very important role in anti-inflammatory response
The most predominant antibody produced in the mucosa
Does not activate macrophages, DCs or complement
There is another class of antibodies called IgD (D for dispensable). So far, no one knows its role
Once you have proper VDJ and VJ, they will then be joined to the correct constant chain
VJ is on the light chain will be joined to either Kappa or Lambda light chain constant regions (depending on which chromosome gave the proper VJ)
VDJ will be joined to the constant region of the heavy chain (the M constant region to give IgM)
causes Abs to bind
causes immune response
what are the roles and properties of T cells
On their surface, they have a receptor for the antigen. This receptor is called TCR (T Cell Receptor)
Properties of the TCR:
Like the antibody, it has two chains
One alpha and one beta … OR
One gamma and one delta
The two chains come together to form a functional TCR
The TCR does NOT recognize soluble antigen the way the antibody (or BCR / B cell receptor) does
Goes through the same combinatorial and junctional diversity as the antibodies
All T cells are mono-specific (like B cells)
The TCR is NOT secreted
T cells either express alpha and beta chains (called alpha-beta T cells) or express gamma and delta chains (called gamma-delta T cells)
We will focus on alpha-beta T cells
Cd4+ T cells needed to activate B cells and CD8+ T cells; CD4 can be activated in different ways to give rise to different phenotypes-->different functions
B cells use perforin and granzyme B (like NK cells) to kill infected and tumor cytotoxic;
The TCR recognizes a COMBINED surface of both MHC and peptide
where are MHC I found?
on all nucleated cells (i.e. not RBCs)
where are MHC II found?
dendritic cells, B cells, and monocytes/macrophages
MHC I is made of one chain + and invariant domain called beta-2-microglobulin
MHC II is made of two chains (alpha and beta)
All MHC genes are co-dominantly expressed (i.e. you will express MHC from both parents)
MHC I vs MHC II function
Presents antigen to CD8+ T cells
Presents antigens synthesized inside the same cell where MHC I is expressed (called endogenous antigens)
Ex: Virus and tumor
Presents antigen to CD4+ T cells
Presents antigens synthesized outside the cell (called exogenous antigens)
The CD4 and CD8 molecules on T cells bind directly to MHC II and MHC I respectively
MHC II activate CD4+ T cells
what are the roles of APC?
activate immune system--> CD4+ T cells