Bakács T, Lutz H U, Tusnády G, Varga L, Merry A H, Sim R R
Department of Immunology, National Institute of Oncology, Budapest, Hungary.
Mol Immunol. 1994 Aug;31(12):901-11. doi: 10.1016/0161-5890(94)90010-8.
Lysis of papain-treated group A and B erythrocytes by human complement was studied by an anti-A (BRIC. 131) and an anti-B (BRIC. 30) IgM monoclonal antibody in 51Cr release assays. The indirect effect of membrane-bound antibody, i.e. its influence on complement binding to sensitized surrounding cells, was examined in a cold target competition test in which sensitized, non-labelled cells are present along with sensitized labelled cells and complement. The mode by which anti-A antibodies indirectly suppressed lysis of sensitized B cells up to 20-fold was studied by following C1q and C3b binding. C1q binding to both types of erythrocytes was not altered in mixed populations of erythrocytes in the presence of both antibodies. Binding of C3b to a mixture of both cell types was, however, suppressed, when both antibodies were present. C3b deposition in mixed cell populations did not reach a significantly higher extent than deposited to one type of erythrocyte alone. This was consistent with the results from competitive lysis and suggests that the anti-A captured most C3b at high anti-A concentrations and deprived the similarly sensitized B erythrocytes of complement. We think that this phenomenon is not due to an uneven removal of complement regulatory proteins from A and B erythrocytes by papain. Instead, the phenomenon might be due to an inherent property of anti-A mAb to better produce nucleation sites for C3 convertases which, upon binding factor B, better compete for the limiting factor D. A mathematical analysis of cold target competition experiment (containing 2430 individual measurements) also shows that the distribution of complement between the competing A and B erythrocyte population is uneven, since it predicts that in any given antibody combination the majority of complement is bound to A erythrocytes. This is consistent with the measured average percentage of lysis.
通过抗 A（BRIC. 131）和抗 B（BRIC. 30）IgM 单克隆抗体，在⁵¹Cr 释放试验中研究了人补体对木瓜蛋白酶处理的 A 组和 B 组红细胞的溶解作用。在冷靶竞争试验中检测了膜结合抗体的间接效应，即在存在致敏的未标记细胞、致敏的标记细胞和补体的情况下，其对补体与致敏周围细胞结合的影响。通过追踪 C1q 和 C3b 的结合，研究了抗 A 抗体间接抑制致敏 B 细胞溶解达 20 倍的方式。在两种抗体存在的情况下，混合红细胞群体中 C1q 与两种类型红细胞的结合均未改变。然而，当两种抗体都存在时，C3b 与两种细胞类型混合物的结合受到抑制。混合细胞群体中 C3b 的沉积程度并不比单独沉积到一种类型红细胞时显著更高。这与竞争溶解的结果一致，表明在高抗 A 浓度下，抗 A 捕获了大部分 C3b，并使同样致敏的 B 红细胞缺乏补体。我们认为这种现象不是由于木瓜蛋白酶对 A 和 B 红细胞补体调节蛋白的去除不均所致。相反，这种现象可能是由于抗 A 单克隆抗体的固有特性，即能更好地产生 C3 转化酶的成核位点，该位点在结合 B 因子后，能更好地竞争有限的 D 因子。对冷靶竞争实验（包含 2430 个单独测量值）的数学分析也表明，竞争的 A 和 B 红细胞群体之间补体的分布是不均匀的，因为它预测在任何给定的抗体组合中，大部分补体都与 A 红细胞结合。这与测得的平均溶解百分比一致。
