Nepomuceno R R, Tenner A J
Department of Molecular Biology and Biochemistry, University of California, Irvine 92697, USA.
J Immunol. 1998 Feb 15;160(4):1929-35.
The complement component C1q can interact with a variety of different cells, resulting in multiple functional consequences depending on the cell type. mAbs R3 and R139, which recognize a 126,000 Mr (reduced) cell surface protein, are able to abrogate the C1q-mediated enhancement of monocyte phagocytosis. The cDNA encoding this C1q receptor that modulates phagocytosis, C1qRP, has recently been cloned. Using a DNA probe based on the coding region of the receptor, Northern blot and RT-PCR analysis of RNA isolated from different cell types showed C1qRP expression in cells of myeloid origin and in endothelial cells, but not in cells of lymphoid origin nor in the HeLa epithelial-like cell line or iliac artery smooth muscle cells. FACS analysis of cell surface expression of C1qRP, as detected by mAb R139 and R3, corresponded in all cases to the mRNA levels detected. Using the anti-C1qRP mAb, the 126,000 Mr receptor was also detected in lysates of human platelets. Interestingly, C1qRP is not expressed by the promyelocytic leukemia cell line HL-60, and differentiation of these cells with various chemical compounds did not induce C1qRP expression. It has been reported that C1q can induce specific receptor-mediated responses in fibroblasts. However, RNA and cell surface expression analysis for C1qRP indicate that this particular C1q receptor is not expressed by either human gingival or human skin fibroblasts. These data demonstrate selective expression of C1qRP in specific cell types and support the hypothesis that there is more than one C1q receptor mediating the diverse responses triggered by C1q.
补体成分C1q可与多种不同细胞相互作用，根据细胞类型产生多种功能后果。单克隆抗体R3和R139可识别一种126,000 Mr（还原型）细胞表面蛋白，它们能够消除C1q介导的单核细胞吞噬作用增强。最近已克隆出编码这种调节吞噬作用的C1q受体C1qRP的cDNA。使用基于该受体编码区的DNA探针，对从不同细胞类型分离的RNA进行Northern印迹和RT-PCR分析，结果显示C1qRP在髓系来源的细胞和内皮细胞中表达，但在淋巴系来源的细胞、HeLa上皮样细胞系或髂动脉平滑肌细胞中不表达。用单克隆抗体R139和R3检测到的C1qRP细胞表面表达的FACS分析结果在所有情况下均与检测到的mRNA水平一致。使用抗C1qRP单克隆抗体还在人血小板裂解物中检测到了126,000 Mr的受体。有趣的是，早幼粒细胞白血病细胞系HL-60不表达C1qRP，用各种化合物诱导这些细胞分化也不会诱导C1qRP表达。据报道，C1q可在成纤维细胞中诱导特异性受体介导的反应。然而，对C1qRP的RNA和细胞表面表达分析表明这种特定的C1q受体在人牙龈或人皮肤成纤维细胞中均不表达。这些数据证明了C1qRP在特定细胞类型中的选择性表达，并支持这样一种假说，即存在不止一种C1q受体介导由C1q触发的多种反应。
