Complement component 1Q subcomponent C (C1qC) is an important part of the C1 complex in the classical activation pathway of the complement system. C1qC contains multiple domains that recognize and bind to pathogen surfaces or antibody-antigen complexes.C1q associates with the proenzymes C1r and C1s to yield C1, the first component of the serum complement system. Thus a functional ELISA assay was conducted to detect the interaction of recombinant human C1qC and recombinant mouse C1r. Briefly, C1qC was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to C1r-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-C1qC pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 μL stop solution to the wells and read at 450/630nm immediately. The binding activity of recombinant human C1qC and recombinant mouse C1r was shown in Figure 1, the EC50?for this effect is 0.049ug/mL.