Human C1 binds to the TiCRT recombinant S domain. (A) rTiS was incubated with human C1, followed by a goat anti-C1 antibody and a rabbit alkaline phosphatase–conjugated anti-goat IgG antibody. (B) As a negative control, rTiS was incubated with 3% phosphate-buffered saline (PBS)/skimmed milk, followed by goat anti-C1 antibody and a rabbit alkaline phosphatase–conjugated anti-goat IgG antibody. (C) As a positive control, C1 was detected with an anti-C1 antibody, followed by a rabbit alkaline phosphatase–conjugated anti-goat IgG antibody.