Effect of C-terminal mutations in FH binding to C3b deposited on beads. (A) C3b was deposited on beads by using purified C3 and factors B and D. C3b deposition was verified by showing increased binding of anti-C3c antibody by flow cytometry. (B-C) FH binding to C3b-bearing beads was competed with wt and several mutant FH19-20 fragments. FH was fluorescently labeled, and binding was analyzed by flow cytometry. (B) Data on FH binding in the presence of FH19-20 mutants of specific interest to this study are shown by dark gray–shaded bars; (C) data for control mutants are shown by light gray–shaded bars. The assays were performed at least 4 times. Shown are average geometric mean fluorescence intensity (GMFI) values (± SD). One-way ANOVA with Tukey’s multiple comparison posttests was performed. *P < .05; **P < .01; ***P < .001. ns, not significant.