斑点叉尾鮰TLR20和TLR21基因在不同细菌和病毒 感染后的表达特征

应用实时荧光定量PCR技术，检测了TLR20和TLR21基因在斑点叉尾鲴Ictalurus punctatus感染迟钝爱德华氏菌Edwardsiella tarda、链球菌Streptococcus iniae、嗜水气单胞菌Aeromonas hydrophila和斑点又尾鲴呼肠孤病毒（Channel Catfish Hemorrhage Reovirus，CCRV）后，在0、12、24、48、72h、7d，肝脏、头肾、脾脏、肠中的时空表达特征。结果显示，4种病原均能引起斑点叉尾鲴TLR20、TLR21基因在所测免疫相关组织中表达量的变化，但呈现出不同的表达模式：感染嗜水气单胞菌后这两种基因的表达差异巨大，而TLR21基因的表达变化不大，在肝脏和头肾中表达量仅在3倍以内变化。感染爱德华氏茵后，TLR20、TLR21两种基因的表达模式类似，在肝脏中表达量显著上调。链球菌引起肝脏TLR20表达量发生4360倍的变化，远远高于TLR21基因在同组织中的表达量（257．8倍）。斑点叉尾鲴呼肠孤病毒感染引起TLR20、TLR21两种基因在肝脏、头肾的上调表达，肠、脾脏的下调表达。以上结果表明了TLR20、TLR21在斑点叉尾鲴天然免疫应答中起重要作用，为研究鱼类疾病防御机制提供了理论参考。

Expression analysis of TLR20 and TLR21 genes in channel catfish Ictalurus punctatus challenged by different bacteria and virus

Toll-like receptor （TLR） is a kind of immune defense, while TLR20 and TLR21 belong pattern recognition receptor with the function of to a specific branch- non-mammalian TLRs. Expression of channel catfish Ictalurus punctatus TLR20 and TLR21 genes in the head kidney, intestine, liver and spleen was tested by quantitative real-time PCR at 0 h, 12 h, 24 h, 48 h, 72 h and 7 d after infection by Aeromonas hydrophila, Edwardsiella tarda, Streptococcus iniae and channel catfishhemorrhage reovirus （CCRV）, respectively. The results showed that all the four pathogens induced the two genes to change their relative expression levels in catfish main immune tissues, and the expression changes were specific. Expression of the two genes was highly different after infection by A. hydrophila. The trends of expression of the two genes were similar after infection by E. tarda, and the expressions were up-regulated in liver. S. iniae induced 4,360-fold change in expression level of TLR20 in liver, much higher than TLR21 （257. 8-fold）. The expression of the two genes was up-regulated in liver and head kidney, while down-regulated in intestine and spleen after infection by CCRV. All the results demonstrated the core function of TLR20 and TLR21 genes in channel catfish. This finding will offer theoretical reference for the study of fish disease defense mechanism and provide a new approach for developing more effective vaccines and immune therapies.