Gordon D L
Department of Clinical Microbiology, Flinders Medical Centre, Adelaide.
Pathology. 1988 Apr;20(2):124-9. doi: 10.3109/00313028809066622.
The requirement for an intact thiolester bond in C3 for assembly of the membrane attack complex and bactericidal activity was demonstrated in a system permitting only alternative pathway activation. Serum depleted of C3 and C4 by treatment with potassium bromide was reconstituted with forms of C3 with an intact (native C3) or disrupted (NH3.C3) thiolester bond, and bactericidal activity against Haemophilus influenzae b was determined. For strain 885 in high-antibody-containing serum, reconstitution with native C3 was associated with marked bactericidal activity (log10 kill in 60 min 1.01 +/- 0.08) compared with reconstitution with NH3.C3 (log10 kill -0.04 +/- 0.19, p less than 0.001). Similar results were obtained with other strains of H. influenzae b. In serum lacking type-specific antibody no alternative pathway-mediated bactericidal activity was detected against any of the strains examined, even when native C3 was added to KBr serum. These experiments indicate how the biochemical structure of C3 directs its functions; only forms of C3 with an intact thiolester bond, which can covalently bind to bacterial surfaces, can serve as the C5 convertase and generate bacterial activity. In addition these experiments demonstrate an absolute antibody dependence for alternative pathway-mediated bactericidal activity against H. influenzae.
在一个仅允许替代途径激活的系统中，证实了补体3（C3）中完整的硫酯键对于膜攻击复合物组装和杀菌活性的必要性。用溴化钾处理使C3和C4耗竭的血清，再用具有完整（天然C3）或断裂（NH3.C3）硫酯键的C3形式进行重构，并测定其对b型流感嗜血杆菌的杀菌活性。对于含高抗体血清中的885菌株，与用NH3.C3重构相比（log10杀伤率-0.04±0.19，p<0.001），用天然C3重构具有显著的杀菌活性（60分钟内log10杀伤率1.01±0.08）。对其他b型流感嗜血杆菌菌株也获得了类似结果。在缺乏型特异性抗体的血清中，即使向KBr血清中添加天然C3，也未检测到针对任何检测菌株的替代途径介导的杀菌活性。这些实验表明C3的生化结构如何指导其功能；只有具有完整硫酯键、能共价结合到细菌表面的C3形式，才能作为C5转化酶并产生细菌活性。此外，这些实验证明了针对b型流感嗜血杆菌的替代途径介导的杀菌活性对抗体的绝对依赖性。
