13- B cell Immunity Flashcards
Activation of the B cell requires what 2 signals?
- Interaction of BCR with antigen
- Interaction of TCR with peptide/MHC complex and interaction between CD40 and CD40L.
For Thymus- independent antigens, the second signal can be provided by the antigen itself and no T cell is required.
What is secreted by the T cell to drive B cells into proliferation?
IL-4, 5, and 6 as well as its own expression of CD40L
Isotype Switching
The changing of the Ig which is secreted during a given response.
Occurs via rearrangement of the Constant region of the heavy chain, during T-dependent responses. Regulated by T-cell cytokines.
Somatic recombination is the key.
Somatic recombination and its key enzyme
Aka switch recombination
Used for Isotype switch
DNA loops out and intervening DNA is excised and is deleted An enzyme called AID (activation-induced cytidiine deaminase) is the key enzyme.
Germinal Centers
Sites of B cell proliferation and differentiation which form during immune responses. Here is where isotype switch, somatic hypermutation of Ig genes and development of memory B cells/plasmablasts (immature plasma cells) occur.
What do primary B cells which enter the germinal center leave as?
Memory B cells or as plasmablasts
T-Independent Response
Use T-independent antigens. The antibodies formed are usually IgM and are not somatically mutated, consequently the antibodies are lower affinity than those of T-dependent antigens.
They are still likely useful for a rapid response to bacterial infection, as most of these antigens are associated with bacterial products..
B cells can be cross linked and triggered to produce antibodies simply by the antigen binding, without the need for T-cells
Somatic Hypermutation
Changing of variable site to allow for more efficient binding to the pathogen.
AID enzyme also plays an important role here
