C4b2bC3转化酶(C3 convertase)形成 C4—C4a,C4b C4b2b C2 C2a, C2b. C4b2b3b C5转化酶每(C5 convertase)形成 C3→C3a,C3b C4b2b C4b2b3bC4b2b—— C3转化酶（C3 convertase）形成 C4b2b3b —— C5转化酶（C5 convertase）形成 C4 C4a，C4b C1qrs C4b2b C2 C2a，C2b C3 C3a，C3b C4b2b C4b2b3b