Ghebrehiwet B
Department of Medicine, State University of New York, Stony Brook 11794-8161.
Behring Inst Mitt. 1989 Jul(84):204-15.
Information gathered from various sources indicates that the receptor for human C1q is expressed on a wide range of normal and cultured cell lines. Similarly, the functions mediated by the C1qR are as diverse as the cells that express the molecule. On B lymphocytes, for instance, the C1qR is known to mediate cellular cytotoxicity, induce an anti-proliferative response, inhibit synthesis of IL-1 and modulate the synthesis of Ig, whereas on PMNs and monocytes the C1qR participates in the increase of oxidative metabolism and enhancement of phagocytosis of opsonized target particles. Endothelial cells which form an important barrier between blood and vascular basement membrane use their C1qR to localize C1q bearing immune complexes into the basement membrane and thus initiate an inflammatory response. Human diploid fibroblasts express two types of C1qRs: a low affinity C1qR for the collagen-like domain and a small subpopulation expressing high affinity C1qR which binds to the globular region of C1q. Since the high affinity subpopulation manifests characteristics of fibroblasts participating in wound healing and tissue regeneration, the C1qR on these cells may play an important role at sites of inflammation. Recently, binding of C1q to the C1qR on mouse fibroblasts was shown to induce chemotaxis and K+ conductance activation with an increase in cytosolic Ca2+. Although isolation of C1qR from every cell type has not been accomplished as yet, partial characterization of highly purified C1qR from Raji cells and platelets indicate that at least on these cell types, the structure of the molecule is similar. Both molecules are anionic, single chain glycoproteins of approximately 67-70 kDA and upon reduction on SDS-PAGE migrate to an apparent 80-85 kDa indicative of the presence of disulfide bonds. The sedimentation coefficient was estimated to be 2.4-4.2S for platelet C1qR and 4.2S for that of Raji. Equilibrium isoelectric focusing showed the Raji cell C1qR to migrate with a pI of 5.5-6.0. Because the Raji C1qR reveals two components when analyzed by two dimensional SDS-PAGE, the possibility that the C1qR may be a doublet of two apparent 70 kDa molecules only one of which contains relatively more intrachain disulfide bonds is being raised.
从各种来源收集的信息表明，人C1q受体在多种正常细胞系和培养细胞系上均有表达。同样，由C1qR介导的功能与表达该分子的细胞一样多样。例如，在B淋巴细胞上，已知C1qR可介导细胞毒性、诱导抗增殖反应、抑制IL-1的合成并调节Ig的合成，而在多形核白细胞和单核细胞上，C1qR参与氧化代谢的增强和调理素化靶颗粒吞噬作用的增强。在内皮细胞中，内皮细胞在血液和血管基底膜之间形成重要屏障，它们利用其C1qR将携带C1q的免疫复合物定位到基底膜中，从而引发炎症反应。人二倍体成纤维细胞表达两种类型的C1qR：一种对胶原样结构域具有低亲和力的C1qR，以及一小部分表达与C1q球状区域结合的高亲和力C1qR的亚群。由于高亲和力亚群表现出参与伤口愈合和组织再生的成纤维细胞的特征，这些细胞上的C1qR可能在炎症部位起重要作用。最近，已证明C1q与小鼠成纤维细胞上的C1qR结合可诱导趋化作用并激活K+电导，同时细胞溶质Ca2+增加。尽管尚未从每种细胞类型中分离出C1qR，但对来自Raji细胞和血小板的高度纯化的C1qR的部分特性分析表明，至少在这些细胞类型上，该分子的结构相似。这两种分子都是阴离子单链糖蛋白，分子量约为67 - 70 kDa，在SDS-PAGE上还原后迁移至约80 - 85 kDa，表明存在二硫键。血小板C1qR的沉降系数估计为2.4 - 4.2S，Raji细胞的C1qR沉降系数为4.2S。平衡等电聚焦显示Raji细胞C1qR以pI为5.5 - 6.0迁移。由于通过二维SDS-PAGE分析时Raji C1qR显示出两个组分，因此有人提出C1qR可能是两个表观分子量为70 kDa的分子的双峰，其中只有一个含有相对较多的链内二硫键。
