Olsen H M, Parish C R, Altin J G
Division of Immunology and Cell Biology, Australian National University, Canberra City.
Immunology. 1996 Jun;88(2):198-206. doi: 10.1111/j.1365-2567.1996.tb00005.x.
Histidine-rich glycoprotein (HRG), a plasma protein that binds heparin and divalent cations, has been implicated in immune regulation through its ability to modulate complement function, macrophage Fc receptor expression and phagocytosis, and its ability to inhibit the proliferation of human peripheral blood T cells in vitro. In the present work we used fluorescence flow cytometry to study the binding of human HRG to the human T-cell lines Jurkat and MT4, and to the murine antigen-specific T-cell clone D10, and to study the effect of divalent cations zinc and copper on this binding. Our results show that HRG binds strongly to these cell lines at 4 degrees, and that the binding is markedly potentiated by physiological concentrations of zinc (20 microM), and to a lesser extent by copper (10 microM). In contrast to previous studies, HRG binding was largely inhibited by 50 micrograms/ml heparin, both in the absence and in the presence of zinc, suggesting that HRG interacts primarily through glycosaminoglycans on the T-cell surface. Studies using confocal fluorescence microscopy indicated that following incubation of MT4 cells with HRG in the presence of zinc at 4 degrees, the HRG was localized exclusively at the plasma membrane, but was actively internalized after incubation at 37 degrees. Interestingly, HRG interfered with the ability of D10 cells to adhere to tissue culture plastic, as well as to laminin-, collagen- or fibronectin-coated culture dishes. This effect was markedly potentiated by 20 microM zinc, and was partially reversed by heparin. The results suggest that zinc markedly potentiates the binding of HRG to T cells, and that HRG and zinc may play an important role in regulating the adhesion of T cells to other cells and the extracellular matrix.
富含组氨酸的糖蛋白（HRG）是一种能结合肝素和二价阳离子的血浆蛋白，因其具有调节补体功能、巨噬细胞Fc受体表达和吞噬作用的能力，以及在体外抑制人外周血T细胞增殖的能力，而与免疫调节有关。在本研究中，我们使用荧光流式细胞术研究了人HRG与人T细胞系Jurkat和MT4、小鼠抗原特异性T细胞克隆D10的结合情况，并研究了二价阳离子锌和铜对这种结合的影响。我们的结果表明，HRG在4℃时能强烈结合这些细胞系，并且生理浓度的锌（20 microM）能显著增强这种结合，铜（10 microM）在较小程度上也有增强作用。与先前的研究不同，无论有无锌存在，50微克/毫升的肝素都能在很大程度上抑制HRG的结合，这表明HRG主要通过T细胞表面的糖胺聚糖相互作用。共聚焦荧光显微镜研究表明，在4℃下锌存在的情况下，MT4细胞与HRG孵育后，HRG仅定位于质膜，但在37℃孵育后会被主动内化。有趣的是，HRG干扰了D10细胞黏附于组织培养塑料以及黏附于层粘连蛋白、胶原蛋白或纤连蛋白包被的培养皿的能力。20 microM的锌能显著增强这种作用，肝素能部分逆转这种作用。结果表明，锌能显著增强HRG与T细胞的结合，并且HRG和锌可能在调节T细胞与其他细胞及细胞外基质的黏附中起重要作用。
