B cell immunity Flashcards
(34 cards)
Mature Naive B cells
BCR: IgM, IgD, Ig alpha & beta
Co-BCR: CD19, CD81, CR2
HLA class II (recognize CD4 helper T)
CD40 & CD 20
naive B2 cells
follicular & marginal (in spleen)
naive B1 cells
mucosa w/ limited Ag specificity
1st signal B cell activation
Ig recognizes Ag, need crosslinking of 2 Ig alpha/beta for signal transduction (via Syk) with CR2 & CD19 tails in cytoplasm (C3d protein helps BCR signaling)
Outcome of 1st signal
more IgM secretion
increase cytokine receptors
increased B7 expression
enhance survival/proliferation
What do B cells express after 1st signal for activation?
increase in CCR7 on surface (to bind CCR7 on T cells)
What is important in the immune synapse between B & T cells?
CD40 on B cell binds CD40L on T cells
B7 on B cell binds CD28 on T cells
T cell recognizes epitope on B cell & then B cell is activated & can proliferate that clone
What is the major outcome of T-dependent immune synapse?
induced expression of AID enzyme essential for class switching of B cell (IgM & IgD to IgE/IgA/etc)
IgM
complement activation
IgG
opsonization & phagocytosis, complement activation, neonatal immunity
IgE, IgG4
need IL-4, immunity v worms & leads to mast cell degranulation (immediate hypersensitivity)
IgA
need cytokines (TGF B)
mucosal immunity (transport IgA thru epithelial cells)
Switch Recombination
occurs post CD40:CD40L ligation, rearranged VDJ gene segment recombines w/ downstream C region gene & DNA in between is deleted (so not cut out during mRNA alternative splicing)
Somatic Hypermutation
intro of A TON of point mutations in switch regions of variable areas of Ig genes, VERY VERY high spontaneous mutation rate, AID converts random Cs to Us
expands Ab repertoire to generate high affinity Ag specific Abs
What Ig do you get w/ IL-4 in class switching?
IgE
What Ig do you get w/ TGF-B in class switching?
IgA
Role of Tfh (T follicular helpers)
ICOS:ICOSL interaction (T to B) that provides cytokines for class switching
Selection Checkpoint
selective survival of B cells w/ highest affinity Abs, occurs in germinal centers, need FDC & Tfh interaction w/ B cells for their survival, Ag comes from FDCs
T cell independent activation
leads to plasma cells (B cells w/ huge ERs & produce lots of Ab/sec)
B1 to direct Ags & B2 to blood-borne polysacc
Memory B cell
can live for long time w/o Ag stimulation, express lots of Bcl-2 (anti-apoptosis)
express CD27 & CD45R on surface
Secondary Immune Response
mediated by memory B cells, rapid response to later exposure to same Ag, mostly by IgG
What Ig helps in contraction of immune response?
IgG !!!! (high conc blocks further Ab production)
What does humoral immunity protect against?
extracell pathogens
What is the role of FcR (Fc receptors)?
bind the Fc region of Ag-Ab complex and tags that cell for opsonization or will activate the cell (depending on cell type)
