Figure 3.

Deposited C3 fragments conceal proximal complement factors and initiating antibodies. Complement deposition and antibody binding on pig red blood cells (pRBCs) were measured by flow cytometry using detection antibodies against C3c (a), C4c (b), or IgG (c). The pRBCs were incubated for 2 hr at 37° in 10% hypogammaglobulinaemia human serum (HHS) as the complement source supplemented with IgG anti‐αGal at 20 mg/l and complement inhibitors as indicated. KRA152 (control nanobody) at 90 mg/l; C1qNb75 (inhibiting C1q docking) at 12 mg/l; hC3Nb2 (binds C3 and blocks the action of the C3 convertases of both classical and alternative pathway) at 90 mg/l, anti‐C5 (eculizumab, binds C5 and blocks the action of the C5 convertases of both classical and alternative pathway) at 50 mg/l, and EDTA at 10 mm. ‘% of pos ctrl’ on the y‐axis denotes experiments containing HHS and IgG anti‐αGal, but no inhibitor. The columns represent the mean of four separate experiments (each represented by a dot). The error bars are 95% confidence intervals. The figure shows that inhibition of C3 cleavage increased the detection of C4b and IgG. IgG detection was also increased by global complement inhibition and inhibition of C1q docking.