W02_B Cells Flashcards
recall the clonal selection theory
lymphocytes develop based on need - only those whose receptors are stimulated continue proliferating to produce clones that target that antigen
what are the 3 functions of antibodies?
neutralization, opsonization, complement activation
why can’t IgM be an opsonin?
there is no IgM Fc receptor on phagocytes, so IgM is solely for activating complement
what is IgA best for?
neutralization. it’s no good at opsonizing and activating complement
where is IgE found?
Fc bound to surfaces of mast cells. antigen binding at Fab region causes degranulation
what is the order of somatic recombination in the chains?
heavy: D+J, +V, +C;
light: V+J, +C
how do pre-B cells progress?
first heavy chain selected, then light chain (kappa then lambda). if failed, then apoptosis. immature B cell makes IgM
what is B cell tolerance?
B cells need to be selected against self-antigens. they develop self-restriction, or tolerance. this is central tolerance in the bone marrow.
how do b cells home?
enter lymph nodes through high endothelial venules
what comprises the B cell co-receptor?
CD19, CR2, CD81
what do b cells do to get T cell help?
once bound to the antigen, they express CD40, which binds to CD40L on the Tfh cell. Tfh cell secretes cytokines to B cell
where is the primary focus of activated B cells?
medullary chords of lymph nodes
what types of Ab do B cells make in the primary foci?
IgM; no help from T cells
where is the germinal center (secondary focus)?
between B cell and T cell zones; IgG made here
what’s in the germinal centers?
activated B cells, helper T cells, follicular dendritic cells (not immune cells)
what happens in the germinal centres?
somatic hypermutation + affinity maturation. as the epitope regions become more specific, B cells can bind to T cells better, and get more signals to survive. thus, only the best and most specific B cells will survive to make antibodies
what is isotype switching?
changing the Fc region to become IgG, IgA, or IgE (from IgM). occurs as recombination of the cluster of C genes after VDJ
which cytokine turns B cells into plasma cells?
IL-10
which cytokine turns B cells into memory B cells?
IL-4
note: plasma cells are terminally differentiated, and will not change any longer. they also have short lifespans
okay.
where are plasma cells found?
bone marrow.
what are BAFF and APRIL?
B cell activation and survival factors; note that excess BAFF can have high Ab production, and anti-BAFF can treat lupus
note: child gets IgG through placenta while still in womb, and IgA through breast milk to coat gastric mucosa post natal
okay.
how do RBCs help to clear immune complexes?
they have CR1 receptors on their surface to pick up antigen, and deliver to spleen and liver, where macrophages pluck immune complexes off the RBCs.
which antibody do you test for in acute infection? in chronic infection?
IgM for acute. IgG for chronic.
what is goodpasture’s syndrome?
antibodies directed against the basement membrane of kidneys
what can C3 and C4 levels in the patient tell us?
low levels may indicate immune complex disease with complement consumption
where are memory B cells?
in bone marrow or circulation
