Week 5: B Cell Activation Flashcards
What do mature B cells have?
- BCR (Ig)
- Circulate in the blood, lymph, and the lymphoid organs until they encounter antigen (Ag)
What happens to the B cell when antigen is stimulated?
B cell will create many clones bearing the same Ag receptor (BCR,Ig) undergoing clonal selection and expansion
What do B cell clones do?
Become plasma cells and memory B cells bearing the same Ag receptor
Describe the process of antibody production by B cells?
- DC take antigen to draining LN and activate antigen-specific naive T cells
- T cells proliferate and differentiate to effector T cells
- Tfh stay in LN and interact with activated B cells
- Gives rise to plasma cells that secrete antibodies specific to antigen
- Antibodies exit the draining LN through efferent lymphatic vessel and into circulation
What are the goals of the B cell response?
- Following B cell activation and clonal expansion, some of these B cells will quickly make antibody (low affinity IgM antibody is made first)
- B cells then undergo a series of changes in order to generate higher affinity and isotype-switched antibodies
- Memory cells are generated to provide long-term protection
What is an epitope?
The part of antigen that an antibody/BCR binds
What are the components of an epitope?
Protein, carb, lipid
What is a multivalent antigen?
An antigen that contains more that 1 epitope or multiple copies of the same epitope
What are the outcomes multivalency?
Increased avidity that combines strength of binding of multiple interactions
How many CDRs does an antibody have?
6
How does the number of CDRs affect the antibody?
Used to contact a given antigen varies based on the properties of the antigen
What are the groups of epitopes?
Linear and discontinuous
What is a linear epitope?
Composed of several successive amino acid residues
What is a discontinuous epitope?
Formed from 2 or more parts of the protein antigen that are separated in the amino acid sequence but are brought together in the tertiary structure of the folded protein
Describe the process of cross linking of surface Ig?
- Surface IgM (BCR) on a naive B cell binds to protein, lipid, or carb epitopes of the antigen on the surface of a microbe
- Multivalent antigens are able to bind to multiple membrane bound IgM (mIgM) causes cross linking
- Clustering and aggregation of the BCRs are due to cross linking leading to the sending of signals to the inside of the B cell through IgA and IgB of BCR
- Signaling leads to gene expression changes that intimate B cell activation
- Additional signals are required to activate the B cell
Describe the components of the B cell co receptor?
- CR2-(CD21) can bind complement components fixed on pathogen
- CD19-acts as the signaling chain in interactions with Iga and Igb of BCR
- CD81-brings CD19 to the surface and organizes the co-receptor on the membrane
- Increases the signal through the BCR by 1000 to 10,000 fold and increases the B cells sensitivity to the antigen.
What are B cell response by distinct antigen types?
T dependent responses
T independent responses
What is TD response?
- Requires help from T cells (CD4+)
What is TI responses?
Doesn’t require T cell help (TI-1 and 2 antigens)
What is a T independent antigen?
Stimulates antibody production without the need for T cell help
What are the classes of B cells that mediate with T independent antigens?
- B1-B cells
- Marginal zone B cells
What are B1-B cells?
Produce IgM antibodies independent of T cell help that bind a broad spectrum of Ag with low affinity
What are marginal zone B cells?
Specialized to respond to blood-borne Ag entering interacting with the immune cells in the spleen