MDA5与TLR3信号转导在IBDV致雏鸡法氏囊免疫损伤中的作用机制

The severe bursal lesions is the key point of the immunosuppression in chikens infected with infectious bursal diaease virus (IBDV), which belongs to double-stranded ribonucleic acid (dsRNA) virus. Melanoma differentiation associated gene 5 (MDA5) and toll-like receptor 3 (TLR3) are the pattern recognition receptor detecting for dsRNA virus. In the context, MDA5 and TLR3 of bursas are considered to play important roles in the immunosuppression mechanism in IBDV-infected chickens and need to be certified experimentally. Two-week-old specific pathogen free chickens were inoculated intraocularly and perorally with standard IBDV strain and live vaccine IBDV, respectively. The dynamic cellular and subcellular localization of MDA5 and TLR3, expression of interrelated signal molecules (including IPS1, MyD88, TRIF, NF-κB and IRF3) and their induced products (including TNF-α, IL-1, IL-6 and IFN ) were detected by the methods of real-time fluorescence quantitative PCR, immune electron microscopy techniques. At the same time, the humoral immunity, cellular immunity and tissue morphologic changes of bursas will be the examinational contents in the chickens with immunoenzyme and traditional pathological techniques. The inherent connections of immunolession and signal transduction of MDA5 and TLR3 in bursas of IBDV-infected chickens will be demonstrated with these results. And then, the immunosuppression mechanism will be interpreted in IBDV-infected chickens from the point of resisting viral pattern recognition as well as signal transduction. This will provide new scientific approaches for IBD control.

IBDV为dsRNA病毒，可造成感染雏鸡法氏囊严重损伤而导致雏鸡发生免疫抑制。本研究从能够特异性识别dsRNA病毒的模式识别受体（MDA5与TLR3）及其信号转导入手，以IBDV感染雏鸡法氏囊损伤为切入点，采用实时荧光定量PCR、免疫电镜、免疫酶及传统病理学方法，检测IBDV感染雏鸡、IBDV中等毒力活疫苗免疫对照雏鸡和空白对照雏鸡法氏囊MDA5与TLR3的定位与表达变化；MDA5与TLR3信号转导通路中衔接蛋白分子（IPS1、MyD88、TRIF）、转录因子（NF-κB、IRF3）及其诱导产物（TNF-α、IL-1、IL-6、IFN）表达变化；体液和细胞免疫以及组织病理变化，明确IBDV感染雏鸡法氏囊免疫损伤与MDA5、TLR3信号转导通路活化的内在联系，进一步从雏鸡体内抗病毒模式识别及信号转导的角度在分子水平阐明IBDV致雏鸡免疫抑制机制，为防制雏鸡IBD提供新的科学思路。

雏鸡法氏囊是双链 RNA 病毒 IBDV 的靶器官，IBD 雏鸡法氏囊损伤会造成雏鸡出现严重的免疫抑制。本项目以雏鸡法氏囊为研究材料，从能够特异性识别 dsRNA 病毒的模式识别受体 MDA5 与 TLR3 及其信号转导入手，采用分子生物学、免疫学及传统病理学方法，对雏鸡感染 IBDV后，其法氏囊 chMDA5 和 chTLR3 表达变化、chMDA5 和 chTLR3信号转导通路相关信号分子及其诱导产物（即促炎症因子/免疫调节因子）表达变化、体液免疫和细胞免疫以及组织病理变化进行检测。结果表明，雏鸡法氏囊内chMDA5 和 chTLR3 信号通路能够被 IBDV 激活，参与 IBDV 感染雏鸡过程，且 chMDA5 和 chTLR3 信号通路活化程度与 IBDV 毒力正相关；IBDV激活雏鸡法氏囊内 chMDA5 和 chTLR3 信号转导通路，诱导细胞因子的释放，导致法氏囊组织发生损伤，并且其损伤程度与 chMDA5 和chTLR3 信号转导通路活化程度相关；同时细胞因子在感染早期参与诱导细胞免疫的发生、在感染晚期参与诱导体液免疫的发生。本研究证实了 chMDA5 和chTLR3 信号通路与 IBDV 感染雏鸡法氏囊损伤密切相关，为进一步研究 IBDV 感染雏鸡致病机制及 IBD 防治提供了科学的试验依据。