L9- B cell effector function Flashcards
What happens to immature B cells recognising self cell surface antibodies in the bone marrow?
They can be rescued by receptor editing or apoptosis.
What happens to immature B cells recognising soluble antibodies in the bone marrow?
They down regulate the B cell receptor expression and become anergic when they migrate to the periphery.
What happens to immature B cells that recognise low affinity non crosslinking self molecules in the bone marrow?
These B cells undergo apoptosis in the periphery.
What happens to immature B cells that have no self reaction?
They encounter antibodies with T cell help in the periphery and are activated successfully.
How are B cells activated?
B cells recognising antigen stop in the T cell zone of peripheral lymphoid tissues.
If an exogenous antigen is present there will be a B-T cell interaction and activation will occur.
What are the 3 signals needed to activate the B cell?
- Antigen
- Activated T helper cell or PRR’s or APC’s - prevents inappropriate activation.
- Cytokines stimulate differentiation of B cells into plasma or memory cells.
What are the types of antigen that can activate B cells?
- T cell dependent
- T cell independent 1
- T cell independent 2
What are the receptors and costimulatory molecules involved in T cell dependent antigens?
B cell receptor, cytokines
CD40 molecule from Th cells
What are the receptors and costimulatory molecules involved in the T cell independent antigens?
B cell receptor, cytokines
Innate immune receptors (TLRs)
BAFF from dendritic cells (type 2)
How does T cell dependent activation of B cells occur?
- B cells process the a antigens from pathogens and presents them on its surface with MHC class 2 molecules.
- Activated CD4+ T cells are recruited and bind to activate the B cells. Helped by CD40.
- B cells activate and differentiate into plasma and memory cells with the help of cytokines.
Which adhesion molecules are involved in B-T contact?
Integrin adhesion molecules
T CELL- LFA1/VLA4—–>
What does CD40 do?
CD40 is a costimulatory molecule expressed on the surface of T cells which binds to its ligand on B cells.
It stimulates B cell differentiation/class switching/proliferation.
Causes release of cytokines from T cell which guide the B cell in its development (tell it what cell to become/what isotype. It also stimulates the development of the germinal centre.
How does TI-1 activation of B cells occur in low concentration?
- B cell recognises antigen on surface of pathogen via BCR (usually bacteria).
- Bacteria normally contain PAMPs on surface which are recognised by PRR’s on B cell surface e.g LPS(bacteria, virus, fungi, protozoan)-TLR4(B cell)
- Produces a monoclonal B cell line.
How does TI-1 activation of B cells occur in high concentration?
- PAMPs on pathogens are recognised by PRR’ s on B cell surface. No signal from BCR is needed.
- Polyclonal B cell line produced.
How does TI-2 activation of B cells occur?
Large repeating molecules (H. influenzae) bind multiple BCR’s on their cell surface causing cross linking and activation.
This signal is strong enough to activate the B cell but it is a short response so no memory cells.
