Okada M, Udaka K, Utsumi S
Mol Immunol. 1985 Dec;22(12):1399-406. doi: 10.1016/0161-5890(85)90063-x.
By following dissociation kinetics of radiolabelled C1q from rabbit IgG antibody-sensitized sheep red blood cells (SRBC) before and after its incorporation in the C1 complex, it was demonstrated that the binding stability is markedly enhanced by the presence of the C1r2-C1s2 subunit of C1 which by itself exhibits no significant binding capacity to immune complexes. The dissociation of C1q was decreased by up to 95%, the extent of decrease being pronounced as the cell surface IgG antibody density increased. However, such a stabilizing effect of C1r2-C1s2 was largely abolished when SRBC sensitized with the dimeric fragment F(acb)2 lacking C gamma 3 was used as the C1 binder, whereas the dissociation rate of uncomplexed C1q from F(acb)2-sensitized cells was similar to that from whole IgG-sensitized cells. It was also shown that, although the C1r2-C1s2 subunit is dissociated selectively from C1 bound to either IgG- or F(acb)2-sensitized cells in the presence of EDTA, it is held on much longer by the former cells than the latter cells. These results were taken to indicate that, although the C1 fixation by immune complexes of IgG is undertaken primarily by the interaction between C1q and the C gamma 2 domain, it is also strengthened by the secondary interaction between the C1r2-C1s2 subunit of C1 and the C gamma 3 domain or a structure which is dependent on the pair of C gamma 3 domains.
通过追踪放射性标记的C1q在掺入C1复合物之前和之后从兔IgG抗体致敏的绵羊红细胞（SRBC）上的解离动力学，结果表明，C1的C1r2 - C1s2亚基的存在显著增强了结合稳定性，而该亚基本身对免疫复合物没有明显的结合能力。C1q的解离减少了高达95%，随着细胞表面IgG抗体密度的增加，减少程度更为显著。然而，当使用缺乏Cγ3的二聚体片段F(acb)2致敏的SRBC作为C1结合物时，C1r2 - C1s2的这种稳定作用在很大程度上被消除，而未复合的C1q从F(acb)2致敏细胞上的解离速率与从全IgG致敏细胞上的解离速率相似。研究还表明，虽然在EDTA存在下，C1r2 - C1s2亚基会从与IgG或F(acb)2致敏细胞结合的C1上选择性解离，但它在前者细胞上保留的时间比在后者细胞上长得多。这些结果表明，虽然IgG免疫复合物对C1的固定主要通过C1q与Cγ2结构域之间的相互作用进行，但C1的C1r2 - C1s2亚基与Cγ3结构域或依赖于一对Cγ3结构域的结构之间的二次相互作用也会增强这种固定作用。
