Daha M R, van Es L A
J Immunol. 1979 Aug;123(2):755-8.
C3 nephritic factor (C3NeF), found in the sera of some patients with membranoproliferative glomerulonephritis, has been shown to be composed of two heavy and two light chains, like IgG; in addition it shares antigenic determinants with IgG. Purified C3NeF binds to the amplification convertase of complement, C3b,Bb, and thereby prevents decay of its C3-cleaving potential. The capability of C3NeF to bind to C3b,Bb was used as a means for purifying C3NeF to homogeneity. The investigation described in this report suggests that binding of C3NeF to C3b,Bb occurs via the Fab portion of the molecule. Pepsin treatment of eight C3NeF preparations resulted in an average loss of 76% of C3NeF functional activity. Papain treatment induced a loss of approximately 90%. The decrease in functional activity could be attributed to the accelerated rate of dissociation of 125I-F(ab')2 and 125I-Fab fragments from stabilized cell-bound C3b,Bb. The dissociation rate of 125I-F(ab')2 from C3b,Bb was comparable with the decay of the functional activity of C3b,Bb stabilized by F(ab')2 or Fab fragments of C3NeF. Although these results suggest that the stabilizing activity of C3NeF is mediated by the Fab portion of the molecule, it was found that the Fc portion also contributes to its functional activity.
C3肾炎因子（C3NeF）存在于某些膜增生性肾小球肾炎患者的血清中，已证明它由两条重链和两条轻链组成，类似于IgG；此外，它与IgG共有抗原决定簇。纯化的C3NeF与补体的扩增转化酶C3b,Bb结合，从而阻止其C3裂解潜能的衰变。利用C3NeF与C3b,Bb结合的能力作为将C3NeF纯化至同质的一种方法。本报告中描述的研究表明，C3NeF与C3b,Bb的结合是通过分子的Fab部分发生的。用胃蛋白酶处理8种C3NeF制剂导致C3NeF功能活性平均丧失76%。用木瓜蛋白酶处理导致约90%的丧失。功能活性的降低可归因于125I-F(ab')2和125I-Fab片段从稳定的细胞结合C3b,Bb上加速解离。125I-F(ab')2从C3b,Bb上的解离速率与由C3NeF的F(ab')2或Fab片段稳定的C3b,Bb功能活性的衰变相当。尽管这些结果表明C3NeF的稳定活性是由分子的Fab部分介导的，但发现Fc部分也对其功能活性有贡献。
