FIGURE 3.

S77 inhibits fH and sCR1 binding to C3 and inhibits fH and sCR1 co-factor activity. A, microtiter plates were coated with C3b, and fH was added in the presence of increasing concentrations of S77 or control Fab. Binding of fH to C3b was determined using an anti-fH antibody and a secondary HRPO-conjugated antibody. Absorbance of the reaction mixture was measured at 450 nm. B, cofactor activity for fI-mediated cleavage of C3b was measured by incubating C3b and fI with fH or increasing concentrations of S77 or control Fab. The mixture was incubated at 37 °C, and the samples were analyzed by gel-electrophoresis and Simply Blue staining. C, S77 inhibits CR1 binding to C3b. Microtiter plates coated with C3b were incubated with sCR1 and increasing concentrations of S77 or control Fab. Binding of sCR1 to C3b was detected with an anti-CR1 primary antibody and an HRPO-conjugated secondary antibody. D, sCR1 cofactor activity was determined as described under B except that fH was replaced by sCR1. Data in A and C are expressed as mean ± S.D. of four repeats.