classic complement pathway

classic complement pathway

Immunology 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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2) C4d is the cleavage product of the activated complement component C4, which is activated and degraded as part of the antibody-mediated classic complement pathway.
Markham et al suggest transient glomerular deposition and clearance of small amounts of immune complexes formed during natural antibody response mechanisms in vivo, which initiates the classic complement pathway resulting in generation and deposition of C4d.
Glomerular C4d deposition indicates in situ classic complement pathway activation, but is not a marker for lupus nephritis activity.