Kacskovics I, Wu Z, Simister N E, Frenyó L V, Hammarström L
Department of Physiology, University of Veterinary Science, Budapest, Hungary.
J Immunol. 2000 Feb 15;164(4):1889-97. doi: 10.4049/jimmunol.164.4.1889.
In the cow, maternal immunity is exclusively mediated by colostral Igs, but the receptor responsible for the IgG transport has not yet been identified. The role of an IgG-Fc receptor (FcRn) that resembles a class I MHC Ag in transporting IgGs through epithelial cells was recently shown in selected species. We now report the cloning and characterization of the bovine FcRn (bFcRn). The cDNA and deduced amino acid sequences show high similarity to the FcRn in other species, and it consists of three extracellular domains, a hydrophobic transmembrane region, and a cytoplasmic tail. Despite the high similarity of the extracellular domains with other species, the bovine cytoplasmic tail is the shortest thus far analyzed. Aligning the known FcRn sequences, we noted that the bovine protein shows a 3-aa deletion compared to the rat and mouse sequences in the alpha1 loop. Furthermore, we found a shorter transcript of the bFcRn reflecting an exon 6-deleted mRNA, which results from an inadequate splice acceptor site in intron 5 and produces a transmembrane-deficient molecule, as was previously demonstrated in the related MHC class I gene family in mouse and humans. The presence of bFcRn transcripts in multiple tissues, including the mammary gland, suggests their involvement both in IgG catabolism and transcytosis.
在奶牛中，母体免疫完全由初乳中的免疫球蛋白介导，但负责IgG转运的受体尚未确定。最近在某些物种中发现，一种类似于I类MHC抗原的IgG-Fc受体（FcRn）在通过上皮细胞转运IgG中发挥作用。我们现在报告牛FcRn（bFcRn）的克隆和特性。cDNA和推导的氨基酸序列与其他物种的FcRn高度相似，它由三个细胞外结构域、一个疏水跨膜区和一个胞质尾组成。尽管细胞外结构域与其他物种高度相似，但牛的胞质尾是迄今为止分析过的最短的。比对已知的FcRn序列，我们注意到与大鼠和小鼠序列相比，牛蛋白在α1环中有一个3个氨基酸的缺失。此外，我们发现bFcRn有一个较短的转录本，反映出一个缺失外显子6的mRNA，这是由于内含子5中剪接受体位点不足导致的，产生了一个缺乏跨膜结构的分子，正如之前在小鼠和人类相关的MHC I类基因家族中所证明的那样。包括乳腺在内的多个组织中存在bFcRn转录本，表明它们参与了IgG的分解代谢和转胞吞作用。
