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BLG 307 (38)
Clare Chua (38)

effector functions of antibodies

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BLG 307
Clare Chua

EFFECTOR FUNCTIONS OF ANTIBODIES determined by constant regions of HC Ig’s in body fluids: IgG – internal IgA – external (on mucosal surfaces) IgM – first one made in reponse to antigen NO hypermutation  low overall affinity 10 binding sites  high AVIDITY IgG – 4 subclasses (varying hinge region flexibility, glycosylation sites) some respond to T-INDEPENDENT antigens (LPS) - IgG2, IgG4 otherwise, predominant reponse is from IgG1 IgA – monomer in serum; active as a DIMER on mucosal surfaces held together by J-CHAIN and SECRETORY Component IgE – heavily glycosylated; mediates allergic reactions Isotype Dependent Effector Functions (depends on HC) - Transport o IgA- mucosal o IgG – placental - Non-inflammatory o all but IgE (neutralization and blocking adherence) - Inflammatory o IgG – phagocytosis/opsonization o IgM/IgG – complement activation o IgE – mast cell activation o IgG - cytotoxicity MUCOSAL TRANSPORT – 3g of IgA made daily; very little enters systemic transport submucosal LYMPHOID FOLLICLE secretes IgA (trachea, for example) GERMINAL CENTER = core consisting of identical B cells epithelial M CELLS phagocytose/pinocytose foreign particles in lumen transport digested antigens into follicle and stim. antibody production mucosal immunity is not the same as serum immunity – “parallel systems” nasally administered poliovirus increases IgA in mucosal secretion NO CHANGE in serum IgA, IgM levels dimerization: J-Chain: connected to IgA Cα3 by disulphide bonds made in B cells SC (secretory component) – produced by MUCOSAL EPITHELIUM 5 globular domains: SC1 – non-covalently binds Cα3 of dimeric IgA (or IgM) SC5 – disulphide bonds to Cα2 cytoplasmic tail – targeting 1) secreted on basolateral surface of epithelium 2) binds dimeric IgA 3) endocytosis 4) transcytosis to apical surface; cytoplasmic tail cleaved 5) secretion *
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