BCR/TCR-based adaptive immune systems arise in the jawed vertebrates, and B cell receptors (BCRs) play an important role in the clonal selection of B cells and their differentiation into antibody-secreting plasma cells. The existence of BCR-like molecule and the activation mechanism of the downstream response are still not clear in invertebrates. In this study, an ancient BCR-like molecule (designated as CgIgR) with an immunoreceptor tyrosine-based activation motif (ITAM) in its cytoplasmic tail was identified from the Pacific oyster Crassostrea gigas to investigate its involvement in immune response. CgIgR could bind different bacteria through five extracellular Ig domains and formed dimers. The activated CgIgR recruited CgSyk to promote CgERK phosphorylation. The CgIgR-mediated signaling promoted the production of immunoglobulin domain-containing proteins (CgICP-2 and CgLRRIG-1) through inducing CgH3K4me2. The produced CgICPs eventually facilitated hemocytes to phagocytize and eliminate V. splendidus. This study proposed that there was an ancient BCR-like molecule and BCR-like signaling in molluscs.

基于BCR / TCR的适应性免疫系统出现在颌骨脊椎动物中，B细胞受体（BCR）在B细胞的克隆选择及其分化为分泌抗体的浆细胞中起着重要作用。在无脊椎动物中，尚不清楚BCR样分子的存在和下游反应的激活机制。在这项研究中，从太平洋牡蛎Crassostrea gigas中鉴定出一种古老的BCR样分子（称为Cg IgR），其胞质尾中带有基于免疫受体酪氨酸的活化基序（ITAM），以研究其参与免疫应答的过程。Cg IgR可以通过五个细胞外Ig结构域结合不同的细菌并形成二聚体。招募的活化Cg IgRCg Syk促进Cg ERK磷酸化。所述CG IGR介导的信号促进了生产含有免疫球蛋白结构域的蛋白（的CG ICP-2和CG通过诱导LRRIG-1）CG H3K4me2。产生的Cg ICPs最终促进了血细胞吞噬和消除了V. splendidus。这项研究表明，软体动物中存在一个古老的BCR样分子和BCR样信号。