Marine Science and Engineering College, Qingdao Agricultural University, Qingdao 266109, China.
National and Local Joint Engineering Laboratory of Freshwater Fish Breeding, Heilongjiang River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Harbin 150070, China; Ministry of Agriculture Key Laboratory of Freshwater Aquatic Biotechnology and Breeding, Heilongjiang River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Harbin 150070, China.
Fish Shellfish Immunol. 2017 Sep;68:272-279. doi: 10.1016/j.fsi.2017.07.021. Epub 2017 Jul 10.
TLRs (Toll-like receptors) are very important pathogen pattern recognition receptors, which control the host immune responses against pathogens through recognition of molecular patterns specific to microorganisms. In this regard, investigation of the turbot TLRs could help to understand the immune responses for pathogen recognition. Here, transcripts of two TLR5 (TLR5a and TLR5b) were captured, and their protein structures were also predicted. Meanwhile, we characterized their expression patterns with emphasis on mucosal barriers following different bacterial infection. The phylogenetic analysis revealed the turbot TLR5 genes showed the closest relationship to Paralichthys olivaceus. These two TLR5 genes were ubiquitously expressed in healthy tissues although expression levels varied among the tested tissues. In addition, the two copies of turbot TLR5 showed different expression patterns after bacterial infections. After Vibrio anguillarum infection, TLR5a was generally up-regulated in intestine and skin while down-regulated in gill, while TLR5b showed a general down-regulation in mucosal tissues. After Streptococcus iniae infection, the TLR5a was down-regulated at 2 h while generally up-regulated after 4 h in mucosal tissues. Interestingly, the TLR5b was up-regulated in intestine while down-regulated in skin and gill after Streptococcus iniae infection. These findings suggested a possible irreplaceable role of TLR5 in the immune responses to the infections of a broad range of pathogens that include Gram-negative and Gram-positive bacteria. Future studies should apply the bacteriological and immune-histochemical techniques to study the main sites on the mucosal tissue for bacteria entry and identify the ligand specificity of the turbot TLRs after challenge.
TLRs（Toll-like receptors）是非常重要的病原体模式识别受体，通过识别微生物特有的分子模式来控制宿主对病原体的免疫反应。在这方面，研究大菱鲆 TLRs 可以帮助了解对病原体识别的免疫反应。在这里，捕获了两个 TLR5（TLR5a 和 TLR5b）的转录本，并预测了它们的蛋白质结构。同时，我们重点研究了黏膜屏障在不同细菌感染后的表达模式。系统发育分析表明，大菱鲆 TLR5 基因与牙鲆的亲缘关系最密切。这两个 TLR5 基因在健康组织中广泛表达，尽管在测试的组织中表达水平有所不同。此外，两种大菱鲆 TLR5 在细菌感染后表现出不同的表达模式。在鳗弧菌感染后，TLR5a 在肠道和皮肤中普遍上调，而在鳃中下调，而 TLR5b 在黏膜组织中普遍下调。在链球菌感染后，TLR5a 在 2 小时时下调，而在黏膜组织中 4 小时后普遍上调。有趣的是，在链球菌感染后，TLR5b 在肠道中上调，而在皮肤和鳃中下调。这些发现表明 TLR5 在对包括革兰氏阴性和革兰氏阳性细菌在内的广泛病原体感染的免疫反应中可能具有不可替代的作用。未来的研究应该应用细菌学和免疫组织化学技术来研究黏膜组织上细菌进入的主要部位，并在受到挑战后确定大菱鲆 TLRs 的配体特异性。
