Rits M, Hiemstra P S, Bazin H, Van Es L A, Vaerman J P, Daha M R
International Institute of Cellular and Molecular Pathology, University of Louvain, Brussels, Belgium.
Eur J Immunol. 1988 Dec;18(12):1873-80. doi: 10.1002/eji.1830181202.
The ability of rat monoclonal IgA, specific for 2,4-dinitrophenyl (DNA), to activate the complement (C) system of the rat was investigated using aggregated IgA or IgA immune complexes (IC). IgA was coated onto a solid phase, and tested for its capacity to bind C3 upon incubation at 37 degrees C in normal rat serum (NRS) in the presence of Mg-EGTA. Binding of C3 was observed dependent on the dose of dimeric (d-), polymeric (p-) and secretory IgA tested. In contrast, little C3 fixation was observed in this system with monomeric (m-) rat IgA or with mouse m- and d-IgA (MOPC315). Soluble and insoluble rat IgA IC were prepared using dinitrophenylated rat serum albumin (DNP8RSA) as antigen (Ag), and assessed for C activation. It was shown that insoluble IC (immune precipitates; IP) containing m-, d- or pIgA of rat origin activate the alternative pathway of rat C, as demonstrated by their capacity to induce C consumption in NRS in the presence of Mg-EGTA. When p- and m-IgA IP were compared for their capacity to activate C, it was found that p-IgA activated C four times as efficiently as m-IgA IP (at 2 mg/ml). Soluble rat IgA IC were prepared in an excess of DNP8RSA, fractionated by gel filtration on Sepharose 6B, and analyzed for C activation and antibody (Ab)/Ag ratio. In contrast to m-IgA IP, soluble m-IgA did not activate C. On the other hand soluble d-IgA IC activated C dependent on their concentration and size: at a concentration of 0.1 mg/ml high-molecular weight d-IgA IC with a high Ab/Ag ratio were four times as efficient as low-molecular weight IC with a low Ab/Ag ratio, and twice as efficient as IP prepared at equivalence. To demonstrate the induction by IgA of the assembly of the terminal membrane attack complex, trinitrophenyl (TNP)-conjugated rat red blood cells (TNP-RRBC) coated with d- or p-IgA were shown to be lysed in NRS in the presence of Mg-EGTA. No lysis of m-IgA-coated TNP-RRBC was observed. The results in this study demonstrate that both soluble and insoluble rat IgA IC activate the alternative pathway of homologous rat C. Alternative pathway activation by soluble rate IgA IC is dependent on the size of the IC. The degree of polymerization of the IgA Ab itself also influences C activation.
利用聚合 IgA 或 IgA 免疫复合物（IC），研究了对 2,4 - 二硝基苯基（DNA）具有特异性的大鼠单克隆 IgA 激活大鼠补体（C）系统的能力。将 IgA 包被在固相上，在存在 Mg - EGTA 的情况下，于 37℃在正常大鼠血清（NRS）中孵育，测试其结合 C3 的能力。观察到 C3 的结合取决于所测试的二聚体（d -）、多聚体（p -）和分泌型 IgA 的剂量。相比之下，在该系统中，单体（m -）大鼠 IgA 或小鼠 m - 和 d - IgA（MOPC315）几乎没有 C3 固定。使用二硝基苯基化大鼠血清白蛋白（DNP8RSA）作为抗原（Ag）制备可溶性和不溶性大鼠 IgA IC，并评估其对 C 的激活作用。结果表明，含有大鼠来源的 m -、d - 或 pIgA 的不溶性 IC（免疫沉淀物；IP）激活大鼠 C 的替代途径，这通过它们在存在 Mg - EGTA 的 NRS 中诱导 C 消耗的能力得以证明。当比较 p - 和 m - IgA IP 激活 C 的能力时，发现 p - IgA 激活 C 的效率是 m - IgA IP 的四倍（在 2 mg/ml 时）。在过量的 DNP8RSA 中制备可溶性大鼠 IgA IC，通过在 Sepharose 6B 上进行凝胶过滤进行分级分离，并分析其对 C 的激活作用和抗体（Ab）/Ag 比值。与 m - IgA IP 相反，可溶性 m - IgA 不激活 C。另一方面，可溶性 d - IgA IC 激活 C 取决于它们的浓度和大小：在 0.1 mg/ml 的浓度下，具有高 Ab/Ag 比值的高分子量 d - IgA IC 激活 C 的效率是具有低 Ab/Ag 比值的低分子量 IC 的四倍，并且是在等价条件下制备的 IP 的两倍。为了证明 IgA 诱导末端膜攻击复合物组装，用 d - 或 p - IgA 包被的三硝基苯基（TNP）偶联大鼠红细胞（TNP - RRBC）在存在 Mg - EGTA 的 NRS 中被证明会发生裂解。未观察到 m - IgA 包被的 TNP - RRBC 的裂解。本研究结果表明，可溶性和不溶性大鼠 IgA IC 均激活同源大鼠 C 的替代途径。可溶性大鼠 IgA IC 对替代途径的激活取决于 IC 的大小。IgA 抗体本身的聚合程度也影响 C 的激活。
