Stafford James L, Wilson Melanie, Nayak Deepak, Quiniou Sylvie M, Clem L W, Miller Norman W, Bengtén Eva
Department of Microbiology, University of Mississippi Medical Center, 2500 North State Street, Jackson, MS 39216, USA.
J Immunol. 2006 Aug 15;177(4):2505-17. doi: 10.4049/jimmunol.177.4.2505.
An FcR homolog (IpFcRI), representing the first such receptor from an ectothermic vertebrate, has been identified in the channel catfish (Ictalurus punctatus). Mining of the catfish expressed sequence tag databases using mammalian FcR sequences for CD16, CD32, and CD64 resulted in the identification of a teleost Ig-binding receptor. IpFcRI is encoded by a single-copy gene containing three Ig C2-like domains, but lacking a transmembrane segment and cytoplasmic tail. The encoded Ig domains of IpFcRI are phylogenetically and structurally related to mammalian FcR and the presence of a putative Fc-binding region appears to be conserved. IpFcRI-related genomic sequences are also present in both pufferfish and rainbow trout, indicating the likely presence of a soluble FcR in other fish species. Northern blot and qualitative PCR analyses demonstrated that IpFcRI is primarily expressed in IgM-negative leukocytes derived from the lymphoid kidney tissues and PBL. Significantly lower levels of IpFcRI expression were detected in catfish clonal leukocyte cell lines. Using the native leader, IpFcRI was secreted when transfected into insect cells and importantly the native IpFcRI glycoprotein was detected in catfish plasma using a polyclonal Ab. Recombinant IpFcRI binds catfish IgM as assessed by both coimmunoprecipation and cell transfection studies and it is presumed that it functions as a secreted FcR akin to the soluble FcR found in mammals. The identification of an FcR homolog in an ectothermic vertebrate is an important first step toward understanding the evolutionary history and functional importance of vertebrate Ig-binding receptors.
在斑点叉尾鮰（Ictalurus punctatus）中已鉴定出一种FcR同源物（IpFcRI），它是首个来自变温脊椎动物的此类受体。利用哺乳动物CD16、CD32和CD64的FcR序列挖掘斑点叉尾鮰的表达序列标签数据库，从而鉴定出一种硬骨鱼免疫球蛋白结合受体。IpFcRI由一个单拷贝基因编码，该基因包含三个免疫球蛋白C2样结构域，但缺少跨膜区段和细胞质尾巴。IpFcRI编码的免疫球蛋白结构域在系统发育和结构上与哺乳动物FcR相关，并且一个推定的Fc结合区域似乎是保守的。河豚和虹鳟中也存在与IpFcRI相关的基因组序列，这表明其他鱼类可能也存在可溶性FcR。Northern印迹和定性PCR分析表明，IpFcRI主要在源自淋巴肾组织和外周血淋巴细胞的IgM阴性白细胞中表达。在斑点叉尾鮰克隆白细胞细胞系中检测到的IpFcRI表达水平明显较低。利用天然信号肽，IpFcRI转染昆虫细胞后可被分泌，重要的是，使用多克隆抗体在斑点叉尾鮰血浆中检测到了天然的IpFcRI糖蛋白。通过共免疫沉淀和细胞转染研究评估，重组IpFcRI可结合斑点叉尾鮰IgM，推测它作为一种分泌型FcR发挥作用，类似于哺乳动物中发现的可溶性FcR。在变温脊椎动物中鉴定出FcR同源物是了解脊椎动物免疫球蛋白结合受体进化历史和功能重要性的重要第一步。
