Fries L F, Gaither T A, Hammer C H, Frank M M
J Exp Med. 1984 Dec 1;160(6):1640-55. doi: 10.1084/jem.160.6.1640.
We have prepared C3b covalently linked to IgG via a hydroxylamine-sensitive bond between the C3b alpha' chain and sites predominantly, but not exclusively, located in the IgG heavy chain. This C3b species displays relative resistance to inactivation by factors H and I when compared with free C3b. This resistance appears to be due entirely to reduced affinity of C3b-IgG for factor H. Resistance to inactivation is not conferred on C3b by binding to another serum glycoprotein of similar size, ceruloplasmin, and may be a special property of IgG. C3b-IgG demonstrates an enhanced capacity to consume serum C3 relative to C3b. These alterations of the behavior of C3b when bound to IgG may in part explain the augmentation of alternative pathway activity by IgG. In addition, IgG-induced protection of C3b might influence both complement-mediated killing and phagocytosis of bacteria, as well as modify the in vivo handling of IgG-containing soluble immune complexes.
我们制备了通过C3bα′链与主要但并非仅位于IgG重链上的位点之间的对羟胺敏感的键共价连接到IgG的C3b。与游离C3b相比，这种C3b物种对因子H和I的失活表现出相对抗性。这种抗性似乎完全是由于C3b-IgG对因子H的亲和力降低。与大小相似的另一种血清糖蛋白铜蓝蛋白结合并不会赋予C3b失活抗性，这可能是IgG的一种特殊性质。相对于C3b，C3b-IgG表现出增强的消耗血清C3的能力。C3b与IgG结合时其行为的这些改变可能部分解释了IgG对替代途径活性的增强作用。此外，IgG诱导的对C3b的保护可能会影响补体介导的细菌杀伤和吞噬作用，以及改变含IgG的可溶性免疫复合物在体内的处理方式。
