Santiago A, Satriano J, DeCandido S, Holthofer H, Schreiber R, Unkeless J, Schlondorff D
Department of Medicine, Albert Einstein College of Medicine, New York 10461.
J Immunol. 1989 Oct 15;143(8):2575-82.
Mesangial cells represent specialized pericytes in the renal glomerulus that contribute to the regulation of a variety of glomerular functions. Recently we and others have shown that cultured mesangial cells bind and take up immune complexes in an Fc-dependent manner leading in turn to generation of PGE2, reactive oxygen, and platelet-activating factor. The present studies were designed to further characterize potential Fc-gamma R on mesangial cells. Binding assays with either monomeric or heat aggregated (HA) [125I] labeled rat subclass-specific IgG were performed at 4 degrees C for 2 h on subcultured rat mesangial cells. Monomeric rat IgG2a, IgG2b, IgG1 and HA IgG2a bound only nonspecifically. Saturable Fc-dependent binding occurred for HA IgG2b and HA IgG1 though maximal binding and affinity were much higher for IgG2b. The presence of an Fc-gamma R was confirmed by surface protein iodination of mesangial cells (MC) and immunoprecipitation with either a polyclonal or mAb 2.4G2 prepared against murine Fc-gamma R. Both antibodies precipitated a 45-kDa iodinated protein band from cultured rat MC that comigrated with that from murine macrophage J774 cells on SDS-PAGE. This protein band also reacted with the polyclonal anti Fc-gamma R antibody on immunoblots. In contrast rat renal papillary epithelial cells were negative. The 45-kDa protein recognized by the rat anti-Fc-gamma R antibody 2.4G2 probably represents the binding site for HA IgG2b, as the 2.4G2 antibody also blocked binding of HA IgG2b. By immunofluorescence microscopy all MC stained positively with the polyclonal anti-Fc-gamma R antibody. A cDNA probe for the Fc-gamma RII-alpha on murine macrophages hybridized to mRNA from cultured rat MC which was of the same size (though less abundant) as that from J774 macrophages. These results further characterize the Fc-gamma R on cultured rat MC, and raise the possibility that the mesangial Fc-gamma R may play a role in the handling of immune-complexes by the renal glomerulus.
系膜细胞是肾小体中的特殊周细胞，有助于调节多种肾小球功能。最近我们和其他人发现，培养的系膜细胞以Fc依赖的方式结合并摄取免疫复合物，进而导致前列腺素E2、活性氧和血小板活化因子的产生。本研究旨在进一步表征系膜细胞上潜在的Fc-γR。在4℃下，用单体或热聚集（HA）[125I]标记的大鼠亚类特异性IgG对传代培养的大鼠系膜细胞进行2小时的结合试验。单体大鼠IgG2a、IgG2b、IgG1和HA IgG2a仅非特异性结合。HA IgG2b和HA IgG1出现了可饱和的Fc依赖结合，尽管IgG2b的最大结合量和亲和力要高得多。通过系膜细胞（MC）的表面蛋白碘化以及用针对小鼠Fc-γR制备的多克隆抗体或单克隆抗体2.4G2进行免疫沉淀，证实了Fc-γR的存在。两种抗体都从培养的大鼠MC中沉淀出一条45 kDa的碘化蛋白带，在SDS-PAGE上与小鼠巨噬细胞J774细胞的蛋白带迁移情况相同。这条蛋白带在免疫印迹上也与多克隆抗Fc-γR抗体发生反应。相比之下，大鼠肾乳头上皮细胞为阴性。大鼠抗Fc-γR抗体2.4G2识别的45 kDa蛋白可能代表HA IgG2b的结合位点，因为2.4G2抗体也能阻断HA IgG2b的结合。通过免疫荧光显微镜观察，所有MC均被多克隆抗Fc-γR抗体阳性染色。小鼠巨噬细胞上Fc-γRII-α的cDNA探针与培养的大鼠MC的mRNA杂交，其大小与J774巨噬细胞的mRNA相同（尽管丰度较低）。这些结果进一步表征了培养的大鼠MC上的Fc-γR，并增加了系膜Fc-γR可能在肾小球处理免疫复合物中发挥作用的可能性。
