Caudwell V, Porteu F, Calender A, Pangburn M K, Halbwachs-Mecarelli L
INSERM U25, Hôpital Necker, Paris, France.
Eur J Immunol. 1990 Dec;20(12):2643-50. doi: 10.1002/eji.1830201218.
Membrane regulatory molecules normally prevent complement activation by autologous cells, therefore we compared the membrane control system of human lymphoid cell lines which activate or not human complement through the alternative pathway (AP). Membrane expression of decay-accelerating factor (DAF), membrane cofactor protein (MCP), complement receptors (CR)1, CR2 and H was measured either by radioimmunoassay or enzyme-linked immunosorbent assay on cell lysates. Soluble extracts of isolated membranes were tested functionally for their ability to accelerate the decay of C3bBb C3-convertase and allow the cleavage of C3b by factor I. Both regulatory functions were detected in solubilized membranes of Ramos cells, which do not activate the AP, as well as on the potent AP activator, Raji. Raji cells were found to express CR2, DAF and MCP molecules, while MCP was the only known regulatory protein detected on Ramos cells which expressed neither CR1, nor CR2, H or DAF. The I-cofactor activity of both Raji and Ramos cells was immunoprecipitated by anti-MCP, but the decay-accelerating activity was not adsorbed by anti-DAF nor by any of the available antibodies. Two EBV genome-negative cell lines (BJAB, BL41) were tested before and after in vitro conversion by EBV. As previously shown, EBV-converted cell lines activate the AP more efficiently than EBV- cell lines. At the same time, EBV superinfection induces an increase of both AP regulatory functions of cell membranes and enhances the expression of DAF, MCP and CR2. The results of this study show that complement activation by lymphoid cell lines is not related to an impaired autologous control of these cells, but that the expression of regulatory molecules increases together with the appearance of activating structures on the cell surface. Our results also suggest the occurrence of a new factor involved in the decay-accelerating activity on BL lines.
膜调节分子通常可防止自体细胞激活补体，因此我们比较了通过替代途径（AP）激活或不激活人补体的人淋巴细胞系的膜控制系统。通过放射免疫测定法或酶联免疫吸附测定法对细胞裂解物中衰变加速因子（DAF）、膜辅因子蛋白（MCP）、补体受体（CR）1、CR2和H的膜表达进行了测量。对分离膜的可溶性提取物进行功能测试，以检测其加速C3bBb C3转化酶衰变以及使I因子裂解C3b的能力。在不激活AP的Ramos细胞的可溶性膜以及强效AP激活剂Raji细胞的膜上均检测到了这两种调节功能。发现Raji细胞表达CR2、DAF和MCP分子，而MCP是在既不表达CR1、CR2、H也不表达DAF的Ramos细胞上检测到的唯一已知调节蛋白。Raji细胞和Ramos细胞的I因子辅因子活性均被抗MCP免疫沉淀，但衰变加速活性既不被抗DAF吸附，也不被任何现有抗体吸附。对两个EBV基因组阴性细胞系（BJAB、BL41）在体外经EBV转化前后进行了测试。如先前所示，EBV转化的细胞系比EBV阴性细胞系更有效地激活AP。同时，EBV超感染会导致细胞膜的两种AP调节功能均增加，并增强DAF、MCP和CR2的表达。本研究结果表明，淋巴细胞系激活补体与这些细胞自身调节受损无关，而是调节分子的表达随着细胞表面激活结构的出现而增加。我们的结果还提示在BL系上存在一种参与衰变加速活性的新因子。
