Effector mechanism

The classic and alternative C3 pathways generate C3b, which serves a number of functions, including interaction of C4b2a (the classic C3 convertase) and C3bBb (the alternative pathway C3 convertase) to allow further activity on C5 and subsequent activation of the terminal sequence (Fig. 1.5). In the final steps, formation of membrane-bound C5b67 permits binding of C8 to the C5 fragment to cause a partial membrane lesion resulting in slow cell lysis. By complexing with C9, the cytolytic reaction is accelerated.