Fig. 4.

Inhibition of cofactor activity by anti-CR1 MoAbs. J3D3 and 3D9 (750 ng) or 5 μl of a 1:500 dilution of the ascites fluid for J3B11, J8B10, and HB8592 were preincubated with 15 ng of sCR1 and then incubated with 500 ng of ¹²⁵I-C3b, with or without the addition of 100 ng factor I. Products were separated by SDS–PAGE under reducing conditions and visualized by autoradiography. The antibodies 3D9 (lane 4) and J3B11 (lane 8) completely blocked and partially inhibited, respectively, the cleavage of the α′-chain to 38- and 64-kD fragments. The other three antibodies had no effect (lanes 6, 10 and 12).