classic complement pathway
classic complement pathwayImmunology The usual route of activation of the complement cascade, initiated by C1q binding to either IgM or to 2 adjacent IgG molecules; the resulting conformational change of C1q autoactivates C1r2, in turn activating C1s2, cleaving C4–C4b followed by C2–C2a; C4b,2a–the C3 convertase of CCP–initiates opsonization, leukocyte chemotaxis, ↑ vascular permeability, and cytolysis; CCP is activated by IgG, IgM, DNA, staphylococcal protein A and C-reactive protein; both classic and alternate pathways are stimulated by trypsin-like enzymes. See Common pathway. Cf Alternate pathway.
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