Fearon D T, Austen K F
J Immunol. 1975 Nov;115(5):1357-61.
The capacity of C3 and 125I-C3 to interact with B and D to generate a C3 convertase was recognized by identification of C3b and Bb on immunoelectrophoresis and 125I-C3b on disc gel electrophoresis. Since the C3 was devoid of C3b as assessed by immunoelectrophoresis, alkaline disc gel electrophoresis, and isoelectric focusing, the initial C3 cleavage was not by the C3b-dependent C3 convertase. In addition, on isoelectric focusing C3 hemolytic activity and the capacity to permit B cleavage by D were isoelectric at pH 6.4, WHEREAS THE CAPACITY OF C3b to permit cleavage by D was isoelectric at pH 5.65. Comparison of the dose-response effects of C3b and C3 for D revealed linear and sigmoidal relationships, respectively, consistent with formation of an initial C3 convertase independent of C3b followed by generation of the C3b-dependent convertase in the reaction initiated with native C3. Further, preincubation of C3 with C3bINA did not diminish its subsequent capacity to permit B inactivation by D as compared to the introduction of C3bINA during the assay, thus supporting the view that native C3, B, and D can form a convertase capable of generating initial C3b.
通过免疫电泳鉴定出C3b和Bb以及在圆盘凝胶电泳上鉴定出125I-C3b，从而认识到C3和125I-C3与B和D相互作用生成C3转化酶的能力。由于通过免疫电泳、碱性圆盘凝胶电泳和等电聚焦评估发现C3不含C3b，所以最初的C3裂解不是由依赖C3b的C3转化酶进行的。此外，在等电聚焦中，C3溶血活性以及允许D裂解B的能力在pH 6.4时呈等电状态，而C3b允许D裂解的能力在pH 5.65时呈等电状态。C3b和C3对D的剂量反应效应比较分别显示出线性和S形关系，这与在天然C3引发的反应中先形成不依赖C3b的初始C3转化酶，随后生成依赖C3b的转化酶一致。此外，与在测定过程中引入C3bINA相比，C3与C3bINA预孵育后，其随后允许D使B失活的能力并未降低，因此支持天然C3、B和D可形成能够生成初始C3b的转化酶这一观点。
