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The Humoral (B cell)
Immune Response
Linked
Recognition
Th2 focus their
activating
cytokines…
(Talin binds to
actin
microfilaments)
Antibody isotype switching:
Switch transcripts produced on both chromosomes
Where do activated B cells
and activated helper T cells
get together?
(trapping)
Freq of lympho’s
specific for given
Ag is 1/1,000,000
Some B cells in the primary focus
become plasma cells
Other B cells form
germinal centers
•Somatic hypermut’n
•Affinity maturation
•Isotype switching
FDCs attract B cells to germinal centers
B cells undergo
somatic
hypermutation,
selection (+ and -)
•1 bp change per
1000 bp per cell
division
•V regions 360 bp
•¾ of changes is
an altered aa
•½ of B cells gets
changed BCR
B cell survival in Germinal
Centers
• Cross-linking of BCRs by Ag
– Ag on FDCs???
– Pathogens multiplying in lymphoid tissue???
• CD40 ligation by T cell CD40L
• Other signals?
– Eg. TNF family cytokines
Thymus-independent 1 Ags (TI-1)
•Induce all B cell division
•Called B cell mitogens
•Eg. LPS
•Unable to induce isotype switching(?), affinity
maturation, or memory cells
TI-2 Ags
•Activate only mature B cells
•Repeating epitopes
•IgM, sometimes IgG
•Eg. Bacterial capsular polysaccharides,
pyogenic bacteria
Transcytosis of
IgA
•Gut, lungs,
tears, saliva,
mammary
•Poly-Ig Rc
•Protection of
epithelial
surfaces
IgG and IgA
can inhibit
viral
infectivity
IgM has two conformations
Ag-bound Ab binds
FcRc with high
avidity
Fc and C3b Rc’s
on phagocytes
Schistomsome larva attacked by eosinophils
ADCC =
antibodydependent cellmediated
cytotoxicity
IgE pre-loaded
on mast cells
Cross-linking
causes mediator
release
•Prostaglandin D2,
leukotriene C4,
TNF-alpha