Complement Activation Pathways
The lectin, classical, and alternative complement activation pathways converge into a final common pathway when C3 convertase cleaves C3 into C3a and C3b.
* C3 convertase complement components are C4b2a (Classical and Lectin pathways) and C3bBb (Alternative pathway).
† C5 convertase complement components are C4b2a3b (Classical and Lectin pathways) and C3bBbC3b (Alternative pathway).
‡ C3a and C5a are both anaphylatoxins.
§ Membrane attack complex complement components are C5b, C6, C7, C8, and C9 (C5b–9).
Ab = antibody; Ag =antigen; C1-INH =C1 inhibitor; MASP = MBL-associated serine protease; MBL = mannose-binding lectin. Overbar indicates activation.