Figure 3.

The hC3Nb1 is a potent inhibitor of the alternative pathway. A, assay in human serum on a zymosan-coated AP activating surface. The horizontal axis gives the concentration of nanobodies present in the serum. The vertical axis shows the level of C3 fragment deposition with 100% deposition defined as the signal from serum without added nanobody. The dotted line indicates the final molar concentration of C3 in the assay based on a concentration of 5.3 μm in undiluted plasma (61). B, multiple sequence alignment of the hC3Nb1 epitope from human C3 and four animals of relevance for animal models for which residues marked with gray shading differ from the human sequence. Colored triangles indicate residues involved in interactions with hC3Nb1. C, assay in mouse serum on a zymosan-coated alternative pathway activating surface depicted as in A. The dotted line represents the final molar concentration of C3 in the assay assuming 4.2 μm C3 in 100% serum from C57BL6 male mice (62).