The classical, lectin, and alternative pathways converge into a final common pathway when C3 convertase (C3 con) cleaves C3 into C3a and C3b. Ab = antibody; Ag =antigen; C1-INH =C1 inhibitor; MAC = membrane attack complex; MASP = MBL-associated serine protease; MBL = mannose-binding lectin. Overbar indicates activation.