Complement activation pathways. The three traditional complement activation pathways converge at complement component C3, leading to the generation of a C5 convertase complex. Cleavage of C5 produces the anaphylatoxin C5a and C5b, initiating formation of the C5b-9 membrane attack complex (MAC). The present study focuses on C3-independent C5 activation pathways shown on the left: activating FcγRs and the coagulation cascade. FcγR, Fc receptor for immunoglobulin G.