Crowell R E, Du Clos T W, Montoya G, Heaphy E, Mold C
Department of Medicine, University of New Mexico School of Medicine, Albuquerque 87131.
J Immunol. 1991 Nov 15;147(10):3445-51.
C-reactive protein (CRP) is an acute-phase protein that binds to components of damage tissue, activates C, and stimulates phagocytic cells. CRP binding to receptors on monocytic and polymorphonuclear phagocytes has been shown. Recently, CRP-binding proteins of 38 to 40 kDa and 57 to 60 kDa have been identified on the human promonocyte cell line U-937 and the mouse macrophage cell line PU5 1.8, respectively. However, analysis of CRP binding to these cells and to peripheral blood leukocytes suggests that additional CRP receptor sites may be present. Because many studies have shown interactions between CRP binding and IgG binding to leukocytes, we have examined further the CRP binding sites on U-937 cells and determined their relationship to the FcR for IgG (Fc gamma R) expressed on these cells. Our results demonstrate specific saturable binding of CRP to peripheral blood monocytes and U-937 cells, which is readily inhibited by aggregated IgG. Monomeric IgG, which binds specifically to Fc gamma RI, inhibited a maximum of 20% of CRP binding to these cells. mAb 197 and mAb IV.3, which block IgG binding to Fc gamma RI and Fc gamma RII, respectively, failed to inhibit CRP binding to U-937 cells. Two CRP-binding molecules were identified by precipitation of lysates from surface-labeled U-937 cells and cross-linking experiments. One of these had a molecular mass of 43 to 45 kDa, similar to the molecule previously described as the CRPR on U-937 cells. The other had the same mobility by SDS-PAGE as Fc gamma RI. The identity of this protein with Fc gamma RI was confirmed by the ability of both IgG-Sepharose and CRP-Sepharose to preclear the protein from cell lysates and by inhibition of binding to both IgG-Sepharose and CRP-Sepharose by anti-Fc gamma RI mAb 197.
C反应蛋白（CRP）是一种急性期蛋白，它能与受损组织的成分结合，激活补体，并刺激吞噬细胞。CRP与单核细胞和多形核吞噬细胞上的受体结合已得到证实。最近，分别在人原单核细胞系U - 937和小鼠巨噬细胞系PU5 1.8上鉴定出了38至40 kDa和57至60 kDa的CRP结合蛋白。然而，对CRP与这些细胞以及外周血白细胞结合的分析表明，可能还存在其他CRP受体位点。由于许多研究表明CRP结合与IgG结合白细胞之间存在相互作用，我们进一步研究了U - 937细胞上的CRP结合位点，并确定了它们与这些细胞上表达的IgG Fc受体（FcγR）的关系。我们的结果表明，CRP能与外周血单核细胞和U - 937细胞发生特异性饱和结合，这种结合很容易被聚集的IgG抑制。特异性结合FcγRI的单体IgG最多只能抑制20%的CRP与这些细胞的结合。分别阻断IgG与FcγRI和FcγRII结合的单克隆抗体197和单克隆抗体IV.3未能抑制CRP与U - 937细胞的结合。通过对表面标记的U - 937细胞裂解物进行沉淀和交联实验，鉴定出了两种CRP结合分子。其中一种分子量为43至45 kDa，与先前描述的U - 937细胞上的CRPR分子相似。另一种通过SDS - PAGE显示与FcγRI具有相同的迁移率。通过IgG - 琼脂糖和CRP - 琼脂糖都能从细胞裂解物中预先清除该蛋白，以及抗FcγRI单克隆抗体197能抑制其与IgG - 琼脂糖和CRP - 琼脂糖的结合，证实了该蛋白与FcγRI的一致性。
