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 = antibody- dependent cell- mediated cytotoxicity

IgE pre-loaded on mast cells Cross-linking causes mediator release Prostaglandin D2, leukotriene C4, TNF-alpha