SAR443809 inhibits AP by blocking cleavage of C3 and FB. (A) SAR443809 inhibits the cleavage of C3 and FB in a dose-dependent manner. In a follow-up experiment to the AP Wieslab EIA, the serum supernatant containing varying amounts of SAR443809, was quenched postactivation on the EIA plate and analyzed by SDS-PAGE, and western blotted for C3a (top) and FB (bottom). (B) SAR443809 inhibits the deposition of C3b on rabbit RBCs in a dose-dependent manner. In an assay set up analogous to AP hemolysis assay, rabbit erythrocytes were incubated with 10% C5-depleted sera in the presence of varying amounts of SAR443809 or IgG4 isotype control. The C3b-deposition on the cells was assessed by flow cytometry. Data reported here is the mean of 2 independent experiments ± standard deviation. (C) SAR443809 inhibits C3 cleavage in solution in factor H depleted sera. Five percent NHS, FH-depleted serum or FH-depleted serum supplemented with FH was incubated with SAR443809. Reactions with the IgG isotype control and with 10 mM EDTA were also included as controls. The samples were quenched and analyzed by SDS-PAGE and western blotted to detect cleavage of the C3 α chain. SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis.