Cell Biology and Immunology Group, Wageningen Institute of Animal Sciences, Wageningen University, PO Box 338, 6700 AH Wageningen, The Netherlands.
Cell Biology and Immunology Group, Wageningen Institute of Animal Sciences, Wageningen University, PO Box 338, 6700 AH Wageningen, The Netherlands.
Dev Comp Immunol. 2014 Apr;43(2):205-22. doi: 10.1016/j.dci.2013.08.010. Epub 2013 Aug 24.
Toll like receptors (TLRs) are present in many different fish families from several different orders, including cyprinid, salmonid, perciform, pleuronectiform and gadiform representatives, with at least some conserved properties among these species. However, low conservation of the leucine-rich repeat ectodomain hinders predictions of ligand specificities of fish TLRs based on sequence information only. We review the presence of a TLR genes, and changes in their gene expression profiles as result of infection, in the context of different fish orders and fish families. The application of RT-qPCR and availability of increasing numbers of fish genomes has led to numerous gene expression studies, including studies on TLR gene expression, providing the most complete dataset to date. Induced changes of gene expression may provide (in)direct evidence for the involvement of a particular TLR in the reaction to a pathogen. Especially when findings are consistent across different studies on the same fish species or consistent across different fish species, up-regulation of TLR gene expression could be a first indication of functional relevance. We discuss TLR1, TLR2, TLR4, TLR5 and TLR9 as presumed sensors of bacterial ligands and discuss as presumed sensors of viral ligands TLR3 and TLR22, TLR7 and TLR8. More functional studies are needed before conclusions on ligands specific to (groups of) fish TLRs can be drawn, certainly true for studies on non-mammalian TLRs. Future studies on the conservation of function of accessory molecules, in conjunction with TLR molecules, may bring new insight into the function of fish TLRs.
Toll 样受体（TLRs）存在于来自多个不同目、包括鲤科、鲑科、鲈形目、鲽形目和鲱形目代表的许多不同鱼类家族中，这些物种中至少存在一些保守特性。然而，富含亮氨酸重复的胞外域的低保守性阻碍了仅根据序列信息预测鱼类 TLR 配体的特异性。我们回顾了 TLR 基因的存在，以及在感染的情况下其基因表达谱的变化，涉及不同鱼类目和鱼类科的情况。RT-qPCR 的应用和越来越多的鱼类基因组的可用性导致了许多基因表达研究，包括 TLR 基因表达的研究，提供了迄今为止最完整的数据集。基因表达的诱导变化可能为特定 TLR 参与对病原体的反应提供（直接或间接）证据。特别是当在同一鱼类物种的不同研究中或在不同鱼类物种中一致时，TLR 基因表达的上调可能是功能相关性的第一个迹象。我们讨论了 TLR1、TLR2、TLR4、TLR5 和 TLR9 作为细菌配体的假定传感器，并讨论了 TLR3 和 TLR22、TLR7 和 TLR8 作为假定的病毒配体传感器。在可以得出关于（鱼类 TLR 组）特定配体的结论之前，还需要进行更多的功能研究，对于非哺乳动物 TLR 的研究尤其如此。未来关于辅助分子（与 TLR 分子一起）功能保守性的研究可能会为鱼类 TLR 的功能带来新的见解。
