Fig. 2

The complement cascades. The three pathways of complement activation are shown. Although each is triggered independently, they merge at the step of C3 activation. The CP is initiated by the binding of antibody to antigen and the lectin pathway by the binding of lectin to a sugar. The alternative pathway turns over continuously and possesses a feedback loop (see Fig. 3). Activation of the complement system leads to inflammation, opsonization, and membrane perturbation. Abbreviations: MASP MBL-associated serine protease, MBL mannose-binding lectin, FB factor B, FD factor D, P properdin