Sialic acid-binding immunoglobulin-like lectins are a family of membrane molecules primarily expressed in immune cells. Most of them are inhibitory receptors containing immunoreceptor tyrosine-based inhibition motifs in the cytoplasmic tail. On the cell surface, sialic acid-binding immunoglobulin-like lectins are mostly bound by sialylated glycans on membrane molecules expressed in the same cell (cis-ligands). Although ligands of sialic acid-binding immunoglobulin-like lectins are not efficiently identified by conventional methods such as immunoprecipitation, in situ labeling including proximity labeling is useful in identifying both cis-ligands and the sialylated ligands expressed by other cells (trans-ligands) of sialic acid-binding immunoglobulin-like lectins. Interaction of the inhibitory sialic acid-binding immunoglobulin-like lectins with cis-ligands including both those with and without signaling function modulates the inhibitory activity of sialic acid-binding immunoglobulin-like lectins by multiple different ways. This interaction also modulates signaling function of the cis-ligands. So far, little is known about the role of the interaction between sialic acid-binding immunoglobulin-like lectins and the cis-ligands. Nonetheless, recent studies showed that the inhibitory activity of CD22 (also known as Siglec-2) is regulated by endogenous ligands, most likely cis-ligands, differentially in resting B cells and those in which B-cell antigen receptor is ligated. This differential regulation plays a role in quality control of signaling-competent B cells and also partial restoration of B-cell antigen receptor signaling in immunodeficient B cells.

中文翻译：

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Siglec 顺式配体及其在免疫系统中的作用。

唾液酸结合免疫球蛋白样凝集素是主要在免疫细胞中表达的膜分子家族。其中大多数是抑制性受体，在细胞质尾部含有基于免疫受体酪氨酸的抑制基序。在细胞表面，唾液酸结合免疫球蛋白样凝集素主要与同一细胞中表达的膜分子（顺式配体）上的唾液酸化聚糖结合。虽然唾液酸结合免疫球蛋白样凝集素的配体不能通过免疫沉淀等常规方法有效鉴定，但原位标记（包括邻近标记）可用于鉴定顺式配体和由其他细胞表达的唾液酸化配体（反式配体）。唾液酸结合免疫球蛋白样凝集素。抑制性唾液酸结合免疫球蛋白样凝集素与顺式配体（包括具有和不具有信号传导功能的顺式配体）的相互作用通过多种不同方式调节唾液酸结合免疫球蛋白样凝集素的抑制活性。这种相互作用还调节顺式配体的信号传导功能。迄今为止，人们对唾液酸结合免疫球蛋白样凝集素与顺式配体之间相互作用的作用知之甚少。尽管如此，最近的研究表明，CD22（也称为 Siglec-2）的抑制活性受到内源配体（最有可能是顺式配体）的调节，在静息 B 细胞和连接 B 细胞抗原受体的细胞中存在差异。这种差异调节在具有信号传导能力的 B 细胞的质量控制以及免疫缺陷 B 细胞中 B 细胞抗原受体信号传导的部分恢复中发挥着作用。