Adaptive Immunity - B Cells Flashcards
What are the two types of adaptive immunity?
Humoral Immunity (B cells) and cell mediated immunity (T cells)
What is an antigen?
An antigen is the target of an immune response
What is an epitope?
The part of the antigen which binds to the receptor
What are the two forms of the B Cell Receptor (BCR - also called Ig and Ab)?
The surface Ig - found on the surface of B cells and the secreted Ig (more commonly called an antibody) which is secreted by plasma cells
Describe the structure of Ig
Consists of two identical heavy chains and two identical light chains. The variable antigen binding region (Fab) is made up of both the heavy and light chains and the constant region (Fc) is just made up of the heavy chains.
What are the 5 isotypes of the constant region?
IgM, IgD, IgG, IgA, IgE
What are the gene sequences in the heavy chain?
variable domain (V), diversity domain (D), joining region (J), constant domain (C)
What are the gene sequences in the light chain?
variable domain (V), joining region (J), constant domain (C)
What are the four main processes for creating diversity in Ig?
- different V regions (40 for heavy, 30-40 for light)
- junctional diversity - adds nucleotides into splice junction using enzyme TdT
- combinatorial diversity - different heavy chain with a different light chain
- somatic hypermutation
What are the two light chain loci?
kappa and lambda
What is the role of bone marrow in B cell development?
Provides signals for maturation and development, allows B cell to proceed through certain checkpoints
What is the final checkpoint in B cell development?
To see if the B cell is self reactive
When does isotype switching occur?
After antigen encounter
What is the purpose of isotype switching?
To increase binding affinity, and because each isotype has a distinct role
What isotypes are good at neutralisation?
IgG, IgA
What isotypes are good at opsonisation?
IgG
What isotypes are good at degranulation?
IgE
What isotypes are good at complement activation?
IgM
What isotypes are good at ADCC?
IgG
In what order do isotypes switch?
IgM, IgG, IgE, IgA
What controls isotype switching?
cytokines released from T helper cells
What isotype does TGF-beta produce?
IgA
What isotype does IL-4 produce?
IgE
What isotype does interferon gamma produce?
IgG
What is affinity maturation?
Dependent on somatic hypermutation in the V region of H and L chains. As antigen levels decrease during an immune response, B cells with mutations that result in high affinity surface Ig are preferentially selected for survival
