Masking of CD22 by cis ligands does not prevent redistribution of CD22 to sites of cell contact
Masking of CD22 by cis ligands does not prevent redistribution of CD22 to sites of cell contact
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DOI：
10.1073/pnas.0400851101
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发表时间：
2004-04-20
影响因子：
11.1
通讯作者：
Paulson, JC
中科院分区：
文献类型：
--
作者：
Collins, BE;Blixt, O;Paulson, JC
CD22是B细胞信号的负调节因子，是Siglec家族的成员，它与糖蛋白上的α2-6连接的唾液酸结合。以前的报道表明，多价唾液酸苷探针与CD22的结合被内源性(Cis)配体阻断或“掩蔽”，除非它们首先被唾液酸酶处理破坏。这些结果表明，B细胞上的顺式配体使CD22在功能上不能与反式配体结合。然而，通过免疫荧光显微镜，我们观察到静止的B细胞上的CD22重新分布到与其他B或T淋巴细胞接触的地方。由于ST6Gall缺失小鼠的淋巴细胞不存在配体缺陷，因此重新分布是通过与相对细胞上的反式配体相互作用来实现的。令人惊讶的是，CD45被认为是CD22的顺式和反式配体，不需要重新分布到细胞接触部位，因为CD22的重新分布独立于CD45，并在CD45缺陷小鼠的淋巴细胞中观察到。此外，CD22的掩蔽不需要CD45，因为在WT和Null小鼠中观察到了类似的掩蔽水平。比较广泛使用的唾液酸苷-聚丙烯酰胺探针和唾液酸苷-链霉亲和素探针，发现后者在没有唾液酸酶处理的情况下结合了B细胞的一个亚群，这表明顺式配体在反式作用中对这两种探针的结合有不同的影响。综合结果表明，与顺式配体的平衡结合并不排除CD22与反式配体的结合，并允许其重新分布到淋巴细胞之间的接触部位。
CD22, a negative regulator of B cell signaling, is a member of the siglec family that binds to alpha2-6-linked sialic acids on glycoproteins. Previous reports demonstrated that binding of multivalent sialoside probes to CD22 is blocked, or "masked," by endogenous (cis) ligands, unless they are first destroyed by sialidase treatment. These results suggest that cis ligands on B cells make CD22 functionally unavailable for binding to ligands in trans. Through immunofluorescence microscopy, however, we observed that CD22 on resting B cells redistributes to the site of contact with other B or T lymphocytes. Redistribution is mediated by interaction with trans ligands on the opposing cell because it does not occur with ligand-deficient lymphocytes from ST6Gall-null mice. Surprisingly, CD45, proposed as both a cis and trans ligand of CD22, was not required for redistribution to sites of cell contact, given that redistribution of CD22 was independent of CD45 and was observed with lymphocytes from CD45-deficient mice. Furthermore, CD45 is not required for CD22 masking as similar levels of masking were observed in the WT and null mice. Comparison of the widely used sialoside-polyacrylamide probe with a sialoside-streptavidin probe revealed that the latter bound a subset of B cells without sialidase treatment, suggesting that cis ligands differentially impacted the binding of these two probes in trans. The combined results suggest that equilibrium binding to cis ligands does not preclude binding of CD22 to ligands in trans, and allows for its redistribution to sites of contact between lymphocytes.