Sgroi D, Varki A, Braesch-Andersen S, Stamenkovic I
Department of Pathology, Massachusetts General Hospital, Charlestown 02129.
J Biol Chem. 1993 Apr 5;268(10):7011-8.
The B lymphocyte cell surface receptor CD22 is an adhesion molecule that can mediate binding to several leukocyte subsets. The first CD22 ligand to be identified was the receptor-linked phosphotyrosine phosphatase CD45, but several lines of evidence suggest that CD22 may interact with multiple counter receptors on adjacent lymphocytes. In the present work, we show that in addition to CD45, a soluble CD22-immunoglobulin fusion protein (CD22Rg) recognizes several other distinct lymphocyte sialoglycoproteins. CD22-mediated adhesion is dependent upon the presence of sialic acids on ligands. CD22Rg is observed to bind specifically to a 115-kDa sialoglycoprotein in COS cells transfected with an alpha-2,6-sialyltransferase cDNA, but not in COS cells transfected with unrelated cDNA clones, indicating that at least some CD22-mediated interactions require presentation of sialic acid in an alpha-2,6 linkage by CD22 ligands. In all cases, truncation of the side chain of sialic acids by mild periodate oxidation abolishes recognition by CD22Rg. Direct binding of CD22Rg to lymphoid cells also requires sialic acids and their side chains. Taken together, these observations indicate that CD22 is a sialic acid-binding lectin and may define a novel functional subset of immunoglobulin superfamily adhesion molecules.
B淋巴细胞表面受体CD22是一种黏附分子，可介导与多种白细胞亚群的结合。首个被鉴定出的CD22配体是受体相关的磷酸酪氨酸磷酸酶CD45，但多项证据表明CD22可能与相邻淋巴细胞上的多种反受体相互作用。在本研究中，我们发现除了CD45外，可溶性CD22-免疫球蛋白融合蛋白（CD22Rg）还能识别其他几种不同的淋巴细胞唾液酸糖蛋白。CD22介导的黏附依赖于配体上唾液酸的存在。在转染了α-2,6-唾液酸转移酶cDNA的COS细胞中，观察到CD22Rg能特异性结合一种115 kDa的唾液酸糖蛋白，而在转染了无关cDNA克隆的COS细胞中则不能，这表明至少某些CD22介导的相互作用需要CD22配体以α-2,6连接方式呈现唾液酸。在所有情况下，用温和的高碘酸盐氧化截断唾液酸侧链会消除CD22Rg的识别。CD22Rg与淋巴细胞的直接结合也需要唾液酸及其侧链。综上所述，这些观察结果表明CD22是一种唾液酸结合凝集素，可能定义了免疫球蛋白超家族黏附分子的一个新的功能亚群。
