FIGURE 1.

AFD blocks activation of C3bB proconvertase. A, SDS-PAGE of proconvertase formation in the presence of catalytically inactive FD (FD(S195A)) and wild-type FD and the effects of blocking (AFD) or non-blocking (8E2) FD antibodies or anti-hepsin (control) Fab fragments. B, AFD fully inhibited C3 proconvertase activation (indicated by the absence of Ba and Bb formation) at a 1:2 molar ratio of AFD to FD. Convertase formation was measured by conversion of FB to C3Ba and C3Bb. C, AFD blocked hemolysis in an assay selective for the alternative pathway. Maximal blockade of hemolysis was achieved at a 1:1 molar ratio of AFD to FD.