Toll-like receptors (TLRs) are known for their essential roles in promotion of innate immunity and induction of adaptive immunity through recognition of pathogen-associated molecular patterns (PAMPs) or danger associated molecular patterns (DAMPs). TLR genes are excellent models for the study of the selective pressure enforced by microorganisms on the host genome. Phylogenetic analyses have shown that interactions between pathogens and immune systems have changed during evolution. Selective pressure for maintenance of specific pathogen recognition has led to evolution of TLRs under both positive and purifying selection. However, intracellular and cell-surface TLRs have been affected differently due to their variation in conservational constraints. In this review, we summarize some of the main studies on the influence of selection on shaping the evolution of several TLR gene families in different terrestrial vertebrate species. We also describe the effect of evolution on the function of different TLRs and their specific conservations in these species and show similarities and differences in evolutionary patterns of TLR orthologs among species as well as among TLR gene families.

Toll样受体（TLRs）通过识别病原体相关分子模式（PAMPs）或危险相关分子模式（DAMPs）在促进先天免疫和诱导适应性免疫中起关键作用而闻名。TLR这些基因是研究微生物对宿主基因组施加的选择性压力的优秀模型。系统发育分析表明，病原体与免疫系统之间的相互作用在进化过程中发生了变化。维持特定病原体识别的选择性压力导致正向和纯化选择下TLR的进化。但是，由于细胞内和细胞表面TLR的保守性差异，它们受到的影响不同。在这篇综述中，我们总结了一些主要的研究，这些研究涉及选择对塑造几种TLR进化的影响不同陆生脊椎动物物种中的基因家族。我们还描述了进化对这些物种中不同TLR的功能及其特定保守性的影响，并显示了物种之间以及TLR基因家族之间TLR直系同源物进化模式的异同。