Fig 1: (A) Comparison of serum Factor H-related protein 5 (FHR-5) levels and serum FHR-5 C3b-binding ability of patients with only FHR-5WT and those carrying FHR-5G278S or FHR-5R356H in ELISA. C3b was immobilized, then serum was added, and FHR-5 was detected by polyclonal anti-FHR-5. Dots represent individual patients. Data are mean of two measurements and are normalized to a calibrator sample containing only FHR-5WT. Subjects expressing FHR-5G278S show a tendency of lower FHR-5 levels and decreased C3b binding compared to the FHR-5WT-expressing group. Serum FHR-5 levels were measured in a sandwich ELISA. Circles represent individual patients. Data are mean of two measurements. (B) Dose-dependent binding of recombinant FHR-5WT, FHR-5G278S, and FHR-5R356H to purified C3b measured in ELISA. The FHR-5G278S variant binds significantly weaker to C3b (one-way ANOVA with Bonferroni’s posttest, p < 0.01). Data are mean of four measurements ± SEM. (C) Interaction of C3b–FHR-5 variants measured by surface plasmon resonance (SPR). C3b in serial dilutions was flown over immobilized FHR-5 variants. The KD of the C3b–FHR-5G278S is one order greater compared to that of C3b–FHR-5R356H and C3b–FHR-5WT. Data are representative of two experiments.