FIG. 3.

(A) Competition of SIC binding to complement proteins by DRS and vice versa. DRS (solid bars) and SIC (open bars) were used to coat microtiter wells and reacted with (a) C6, C6 and DRS, or C6 and SIC or (b) C7, C7 and DRS, or C7 and SIC, as indicated. Each set had a no-coat control (gray bars) in which the wells were not coated with either SIC or DRS. (B) Comparison of competitive inhibition by SIC and DRS of SIC binding to the C6 protein. Wells were coated with 10 μg of SIC and reacted with C6 that had been incubated with various concentrations of SIC (▪) or DRS (▴), as indicated. In the absence of the competitors, SIC and DRS bound to the C6 protein and had an optical density at 450 nm of 0.802 and 0.787, respectively, after subtraction of the respective backgrounds (0.126 and 0.154, respectively).