Activation of C1r

C1 activation requires interaction with two separate Fc domains, so pentavalent IgM antibody is far more efficient at complement activation than IgG antibody (Muller-Eberhard and Kunkel 1961). Antibody binding results in a conformational change in the C1r component of the C1 complex and a proteolytic cleavage of C1r, activating it (Ziccardi and Cooper 1976). This reaction is irreversible under physiological conditions.

C1激活需与两个独立的Fc区域相互作用，因此五价的IgM抗体在补体激活方面的效率远高于IgG抗体（Muller-Eberhard 和 Kunkel 1961）。抗体结合导致C1复合物中的C1r成分发生构象变化，并引发C1r的蛋白酶解切割，从而激活之（Ziccardi 和 Cooper 1976）。在生理条件下，此反应不可逆。