Active Complement Component 1, Q Subcomponent A (C1qA)

Figure. The binding activity of C1qA with CRP.
The complement component 1q (C1q) is composed of 18 polypeptide chains: six A-chains, six B-chains, and six C-chains. Complement Component 1, Q Subcomponent A (C1qA) is six A-chains of C1q. Complement component 1q (C1q is a protein complex involved in the complement system, which is part of the innate immune system. C1q together with C1r and C1s form the C1 complex. It is potentially multivalent for attachment to the complement fixation sites of immunoglobulin. The sites are on the CH2 domain of IgG and, it is thought, on the CH4 domain of IgM. IgG4 cannot bind C1q, but the other three IgG types can. Besides, C Reactive Protein (CRP) has been identified as an interactor of C1qA, thus a binding ELISA assay was conducted to detect the interaction of recombinant human C1qA and recombinant human CRP. Briefly, C1qA were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100μL were then transferred to CRP-coated microtiter wells and incubated for 2h at 37℃. Wells were washed with PBST and incubated for 1h with anti-C1qA pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody, wells were aspirated and washed 3 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50µL stop solution to the wells and read at 450nm immediately. The binding activity of C1qA and CRP was shown in Figure 1, and this effect was in a dose dependent manner.