Xia Pingan, Liu Yusong, Liu Xiaoping, Zhang Zhiyuan, Duan Erzhen, Lu Xiaoyan, Zhao Jun, Cui Baoan
College of Animal Husbandry and Veterinary Medicine, Henan Agricultural University, No. 95 Wenhua Road, Zhengzhou 450002, China.
Vet Immunol Immunopathol. 2011 May 15;141(1-2):144-50. doi: 10.1016/j.vetimm.2011.02.003. Epub 2011 Feb 12.
Receptors for the Fc fragment of IgG (FcγRs) constitute one of the main effector mechanisms through which IgG immune complexes exert their action. Four FcγRs, FcγRI (CD64) with high affinity, FcγRI with intermediate affinity, FcγRII (CD32) and FcγRIII (CD16) with low affinity, have been identified. There are three FcγRII isoforms (activating FcγRIIa and FcγRIIc, and inhibiting FcγRIIb) existing in humans, one isoform in mice (inhibiting FcγRIIb), and two isoforms in cattle (inhibiting FcγRIIb, activating FcγRIIc). Two splice sub-isoforms of FcγRIIb, FcγRIIb1(b1) and FcγRIIb2(b2), have been identified in humans, mice and cattle, however, few of FcγRIIb sub-isoforms have been investigated in pig. In this study, we describe the molecular cloning, sequencing and characterization of a porcine FcγRIIb sub-isoform, FcγRIIb1. The cDNA encoding porcine FcγRIIb1 was isolated from peripheral blood leucocytes RNA with RT-PCR. The porcine FcγRIIb1 cDNA contains a 951bp open-reading frame, encoding a 316 amino acid transmembrane glycoprotein composed of two immunoglobulin (Ig)-like extracellular domains, a transmembrane region and a cytoplasmic tail with an immunoreceptor tyrosine-based inhibiting motif (ITIM). The porcine FcγRIIb1 shares 98.3% homology and has a 19 amino acid in-frame insertion in cytoplasmic tail when compared with amino acid sequence of DQ026064. Immunofluorescence analysis showed that the glycoprotein encoded by the porcine FcγRIIb1 cDNA was expressed in the stable transfected COS-7 cells, and an immunoglobulin-binding assay showed that it had binding activity for IgG immune complexes. Identification of the porcine FcγRIIb1 will help our understanding of the molecular basis of IgG-FcγR interaction in the porcine immune response.
免疫球蛋白G（IgG）的Fc片段受体（FcγRs）构成了IgG免疫复合物发挥作用的主要效应机制之一。已鉴定出四种FcγR，即高亲和力的FcγRI（CD64）、中等亲和力的FcγRII、低亲和力的FcγRII（CD32）和FcγRIII（CD16）。人类存在三种FcγRII亚型（激活型FcγRIIa和FcγRIIc，以及抑制型FcγRIIb），小鼠有一种亚型（抑制型FcγRIIb），牛有两种亚型（抑制型FcγRIIb、激活型FcγRIIc）。在人类、小鼠和牛中已鉴定出FcγRIIb的两种剪接亚型，即FcγRIIb1（b1）和FcγRIIb2（b2），然而，在猪中对FcγRIIb亚型的研究较少。在本研究中，我们描述了猪FcγRIIb亚型FcγRIIb1的分子克隆、测序及特性分析。通过逆转录聚合酶链反应（RT-PCR）从外周血白细胞RNA中分离出编码猪FcγRIIb1的cDNA。猪FcγRIIb1 cDNA包含一个951bp的开放阅读框，编码一个由两个免疫球蛋白（Ig）样细胞外结构域、一个跨膜区和一个带有基于免疫受体酪氨酸抑制基序（ITIM）的胞质尾组成的316个氨基酸的跨膜糖蛋白。与DQ026064的氨基酸序列相比，猪FcγRIIb1具有98.3%的同源性，且在胞质尾中有19个氨基酸的框内插入。免疫荧光分析表明，猪FcγRIIb1 cDNA编码的糖蛋白在稳定转染的COS-7细胞中表达，免疫球蛋白结合试验表明它对IgG免疫复合物具有结合活性。猪FcγRIIb1的鉴定将有助于我们理解猪免疫反应中IgG-FcγR相互作用的分子基础。
