免疫抑制性受体TIGIT介导弓形虫特异性CD8+T细胞衰竭及其逆转机制研究

T cell exhaustion induced by Toxoplasma gondii is an important immune evasion strategy for T. gondii to evade the host cell immune response. Increased expression of T cell inhibitory receptors on the surface of T cells is an important internal cause of T cell exhaustion. T cell immunoreceptor with Ig and ITIM domains (TIGIT) is one newly discovered inhibitory immunoreceptor in recent years. The expression profile of TIGIT on the surface of T. gondii-specific CD8+ T cells and whether TIGIT mediates CD8+ T-cell exhaustion in chronic T. gondii infection as well as other immunoreceptors are not clear. Hence, in this study, the expression percentages of TIGIT and CD226 on T. gondii-specific CD8+ T cells, phenotypic and functional characteristics of TIGIT+CD8+ T-cells in different tissues of mice were examined by flow cytometry during chronic T. gondii infection. Meanwhile, the histopathological score and the parasite load in different tissues of mice were determined by the histopathological analysis and quantitative PCR, respectively. The survival of mice also were recorded. To further test whether blockade of the TIGIT pathway dramatically reinvigorated this exhausted CD8+ T-cell response. The above-mentioned indicators were detected again after administration of anti-TIGIT monoclonal antibody. This project would be helpful to understand the mechanism of TIGIT mediated T. gondii-specific CD8+ T-cell exhaustion and reinvigoration during chronic T. gondii infection, which contribute to design new therapeutic targets to restore the function of CD8+ T cells, and may provide a new research idea for the effective prevention and treatment of T. gondii infection.

诱导宿主T细胞衰竭是弓形虫逃避宿主细胞免疫的一种重要策略。T细胞表面抑制性受体的表达增高是T细胞衰竭的重要内因。作为近年新发现的一种T细胞抑制性受体，TIGIT在弓形虫特异性CD8+T细胞表面的表达特点及其是否介导弓形虫特异性CD8+T细胞的衰竭尚不清楚。因此本研究拟以慢性弓形虫感染小鼠为研究对象，①利用流式细胞术、Real-time PCR等技术检测不同感染时期不同组织中CD8+T细胞表面TIGIT和CD226的表达、TIGIT+CD8+T细胞表型和效应功能的改变、组织的病变程度、组织中虫荷和小鼠的存活情况，探究TIGIT是否介导弓形虫特异性CD8+T细胞的衰竭及其与疾病进程的相关性；②应用抗体阻断TIGIT通路，检测衰竭的CD8+T细胞是否发生功能逆转。以期阐明TIGIT介导弓形虫特异性CD8+T细胞衰竭的发生和逆转机制，为更有效地防治弓形虫感染提供新思路。

诱导宿主T细胞衰竭是弓形虫逃避宿主细胞免疫的一种重要策略。T细胞表面抑制性受体的表达增高是T细胞衰竭的重要内因。作为近年新发现的一种T细胞抑制性受体，TIGIT在弓形虫特异性CD8+和CD4+T细胞表面的表达特点及其是否介导弓形虫特异性CD8+和CD4+T细胞的衰竭尚不清楚。本研究以急、慢性弓形虫感染小鼠为研究对象，运用流式细胞术、Real-time PCR等技术检测不同感染时期不同组织中CD8+和CD4+T细胞表面TIGIT和CD226的表达、TIGIT+CD8+T细胞和TIGIT+CD4+T细胞表型和效应功能的改变、组织的病变程度、组织中虫荷和小鼠的存活情况，探究TIGIT是否介导弓形虫特异性T细胞的衰竭及其与疾病进程的相关性；构建TIGIT-/-小鼠和应用抗体阻断TIGIT通路，检测TIGIT通路对弓形虫感染进程的影响。结果发现在慢性弓形虫感染过程中，小鼠脑组织和脾脏中CD8+和CD4+T细胞表面TIGIT和CD226的表达显著升高，细胞毒作用在感染后期显著降低，同时脾脏中弓形虫特异性TIGIT+TCM细胞被激活并转化为TIGIT+TEM细胞；急性弓形虫感染小鼠脾脏和PBMC中CD8+和CD4+T细胞表面TIGIT的表达在感染早期降低，而在感染晚期显著升高，同时脾脏中弓形虫特异性TIGIT+TCM细胞被激活并转化为TIGIT+TEM细胞；TIGIT的表达与急慢性弓形虫感染小鼠脾脏中的病变以及慢性弓形虫感染小鼠脑组织的病变呈正相关；TIGIT基因的敲除和抗体治疗性阻断TIGIT通路均可减缓弓形虫感染进程和减轻感染负担，为临床弓形虫病的干预提供了理论依据。