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可溶性FcγR同源蛋白抑制香鱼脾细胞产生IgM抗体

A soluble FcγR homolog inhibits IgM antibody production in ayu spleen cells

  • 摘要: 经典Fc受体(Fc receptors, FcRs)结合与识别抗体Fc部分(fragment crystallized, Fc),从而在免疫反应中发挥重要作用。但迄今为止,在鱼类中仅发现哺乳动物可溶性FcR同源蛋白,而且对这类蛋白在鱼类免疫反应中的作用知之甚少。本研究克隆得到一种编码香鱼(Plecoglossus altivelis, ayu)可溶性FcγR同源基因(solubleFc receptor for IgG homolog, PaFcγRl)的cDNA序列,并命名为香鱼FcγR样(ayu FcγR like, PaFcγRl)基因。预测蛋白仅有2个C2型免疫球蛋结构域,不具有跨膜区与胞内区。PaFcγRl基因转录本在各组织广泛表达,但转录水平较低。鳗弧菌(Vibrio anguillarum)感染香鱼后,PaFcγRl基因转录本的表达均显著上调。并且PaFcγRl蛋白可在香鱼头肾、体肾、中性粒细胞中被检测到。随后,在哺乳动物细胞中表达重组PaFcγRl蛋白(recombinant PaFcγRl, rPaFcγRl),结果显示rPaFcγRl蛋白分泌至细胞外,而且在感染后的香鱼血清中检测到PaFcγRl蛋白。进一步通过细胞转染实验证明PaFcγRl可与香鱼IgM结合。最后改良的溶血空斑实验表明重组PaFcγRl成熟肽(recombinant mature protein of PaFcγRl, rPaFcγRlm)具有抑制香鱼脾细胞抗绵羊红细胞(sheep red blood cell, SRBC)体外初次免疫的活性。总之,本研究揭示了PaFcγRl与香鱼脾细胞产生IgM的负调控密切相关。

     

    Abstract: Classical Fc receptors (FcRs) mediate the binding to and recognition of the Fc portion of antibodies and play an important role during immune responses in mammals. Although proteins similar to soluble FcRs have been identified in fish, little is known about the role of such proteins in fish immunity. Here, we cloned a cDNA sequence encoding a soluble Fc receptor for an immunoglobulin G (FcγR) homolog from ayu (Plecoglossus altivelis) (PaFcγRl). The predicted protein was composed of two immunoglobulin C2-like domains but lacked a transmembrane segment and a cytoplasmic tail. The PaFcγRl transcripts were distributed at low levels in all tested tissues, but significantly increased after Vibrio anguillarum infection. The PaFcγRl protein was expressed in the head kidney, trunk kidney, and neutrophils. Recombinant PaFcγRl (rPaFcγRl) was secreted when transfected into mammalian cells and the native protein was also detected in serum upon infection. rPaFcγRl was also demonstrated to bind to ayu IgM, as assessed by cell transfection. Suppressive activity of the recombinant mature protein of PaFcγRl (rPaFcγRlm) on in vitro anti-sheep red blood cell (SRBC) responses was detected by a modified hemolytic plaque forming cell assay. In conclusion, our study revealed that PaFcγRl is closely involved in the negative regulation of IgM production in the ayu spleen.

     

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