Kochi S K, Johnson R C, Dalmasso A P
Department of Microbiology, University of Minnesota Medical School, Minneapolis.
J Immunol. 1991 Jun 1;146(11):3964-70.
Lyme disease is a multisystemic illness caused by the spirochete Borrelia burgdorferi. In the absence of specific antibody, the spirochete is resistant to the bactericidal activity of C, despite the capacity of B. burgdorferi to activate both C pathways. We examined the mechanism of serum resistance by measuring the deposition of C3 and terminal C components on B. burgdorferi in the presence and absence of immune IgG. In normal human serum antibody-sensitized borreliae bound similar amounts of C3, and similar or increased amounts of C8 and C9, in comparison to unsensitized bacteria. However, at comparable levels of C3, C8, or C9 uptake, only sensitized bacteria were killed. The requirement of antibody for killing could not be explained by differences in the rate of C deposition or by differences in the C9 to C8 ratio in the membrane attack complex (MAC). We found that bacteria incubated in C5-depleted human serum, but not in C6-depleted serum, were killed when this treatment was followed by antibody and the missing C components. Bacteria were also killed by reactive lysis (C5b-9) provided that antibody was present. Therefore, the effect of bactericidal IgG occurred at the stage of C5b binding to the bacterial surface. Elution studies of bound C9 indicated that the MAC was stably bound to the outer membrane of B. burgdorferi, whether or not the bacteria were treated with antibody. However, treatment with 0.1% trypsin released 48% of 125I-C9 from the surface of unsensitized borreliae and 24% from IgG-sensitized cells, demonstrating that the presence of the antibody changed the accessibility to trypsin of C9 in the MAC. These results indicate that the effect of antibody in the killing process is not to enhance the rate or extent of initial or terminal component binding, but rather to alter the bacterial outer membrane to allow effective MAC formation.
莱姆病是一种由螺旋体伯氏疏螺旋体引起的多系统疾病。在缺乏特异性抗体的情况下，尽管伯氏疏螺旋体能够激活补体的两条途径，但该螺旋体对补体C的杀菌活性具有抗性。我们通过测量在有或没有免疫IgG存在的情况下，补体C3和补体末端成分在伯氏疏螺旋体上的沉积，来研究血清抗性的机制。与未致敏的细菌相比，在正常人血清中，抗体致敏的疏螺旋体结合了相似量的C3，以及相似或增加量的C8和C9。然而，在C3、C8或C9摄取水平相当的情况下，只有致敏细菌被杀死。抗体对于杀菌的需求不能通过补体沉积速率的差异或膜攻击复合物（MAC）中C9与C8比例的差异来解释。我们发现，在C5缺陷的人血清中孵育的细菌，而不是在C6缺陷血清中孵育的细菌，在这种处理后再加入抗体和缺失的补体成分时会被杀死。只要有抗体存在，细菌也会被反应性溶解（C5b-9）杀死。因此，杀菌性IgG的作用发生在C5b与细菌表面结合的阶段。对结合的C9进行洗脱研究表明，无论细菌是否用抗体处理，MAC都稳定地结合在伯氏疏螺旋体的外膜上。然而，用0.1%胰蛋白酶处理后，未致敏疏螺旋体表面48%的125I-C9被释放，IgG致敏细胞表面24%的125I-C9被释放，这表明抗体的存在改变了MAC中C9对胰蛋白酶的可及性。这些结果表明，抗体在杀伤过程中的作用不是提高初始或末端成分结合的速率或程度，而是改变细菌外膜以允许有效的MAC形成。
