Fig. 1.

Model of complement activation and effector functions. Activation of the complement cascade is initiated by either the classical, lectin, or alternative pathway, but all result in the effector functions of surface opsonization [C3b deposits on the pathogen (yellow) signaling engulfment by a phagocyte], leukocyte recruitment (C3a and C5a), and pathogen lysis by formation and insertion of the C5b-9 complex in membranes (MAC, membrane attack complex) [Permission obtained from Elsevier, (Bohlson et al. 2007)].