Toll样受体信号通路在两栖类中的研究进展

两栖类处于脊椎动物由水生向陆生进化的过渡阶段,进化地位重要。近年来因疾病的爆发、生境破碎化、环境污染、紫外辐射增加、人为过度捕捉和生物入侵等诸多因素引起的全球范围内两栖类种群数量锐减已引起人们的广泛关注。Toll样受体(Toll-like receptor,TLR)家族是一类从线虫到哺乳动物普遍存在的高度保守的模式识别受体(PRRs),可以识别侵入机体病原体的病原相关分子模式(PAMPs),是两栖类先天性免疫防御系统的重要组成部分。本文结合近些年国内外对两栖类TLRs的研究对两栖类TLRs结构特征、进化特点、在两栖类发育早期的差异表达特征和两栖类TLRs信号通路中相关分子的表达研究进行概述。目前对于两栖类TLRs的研究发现两栖类TLRs兼具鱼类和哺乳类TLRs的特征,并在从鱼类到两栖类到哺乳类的进化过程中,TLRs家族部分成员如TLR2的配体识别功能可能发生了一定程度的特化;在两栖类早期发育阶段,获得性免疫不够完善,以TLRs为主的先天免疫防御系统在抵御病原体的侵袭方面发挥了重要作用;在特定病原菌和病毒的胁迫下,可能激活了TLRs下游不同的途径参与两栖类对病原体的免疫应答反应。

Advances in the Study of the Toll-Like Receptor Signal Pathway in Amphibians

Amphibians are transitional species from aquatic to terrestrial lifeforms,which are key to understanding of evolutionary history.In recent years,global amphibian populations have sharply declined,presumably due to outbreaks of infectious diseases,habitat fragmentation,environmental pollution,increasing intensity of ultraviolet radiation,overharvesting,and biological invasion.The declines have aroused widespread concern.Toll-like receptors(TLR)form a class of highly conserved pattern recognition receptors(PRRs)that recognize pathogen associated molecular patterns(PAMPs).Animals from nemathelminths to mammals are considered to possess TLR genes.TLRs are key components of the amphibian innate immune system.We reviewed domestic and international literature on amphibian TLR research.Here,we discuss the structure,evolutionary traits,differential expression during the early stage of amphibian embryo development,and the expression of related molecular structures in TLR signaling pathways in amphibians.We found that amphibian TLRs possess features of both fish-and mammalian-type TLRs.The ligand recognition ability of TLR2(a member of the TLR family)was specialized in the evolutionary process from fish to amphibians and mammals.The larva of amphibians always has incomplete acquired immunity and TLRs are important in resisting the invasion of pathogens during the larval stage.Perhaps different signal pathways are activated to participate in immune responses of amphibians to the presence of various bacteria and viruses.