IRF8/PD-L1通路在烟草暴露树突状细胞调控T淋巴细胞介导肺部炎症中的作用及机制研究

We have previously demonstrated that dendritic cells (DCs) play a pivotal role in T lymphocytes-mediated lung inflammation. However, the mechanisms by which DCs regulating T lymphocyte responses in the context of chronic cigarette smoke exposure, especially the negative regulation, are unclear. Recent studies revealed that PD-L1 was over-expression on DCs in tumor microenvironment, which subsequently drove T cell exhaustion. Therefore, we speculate that the down-regulation of PD-L1 on DCs might represent an important mechanism that T lymphocytes over-activation in the setting of chronic cigarette smoke exposure. However, the expression of PD-L1 on DCs and its modulating mechanisms in chronic inflammation induced by cigarette smoke exposure are largely unknown. In the current study, we sought to evaluate the expression of PD-L1 on DCs and its relation with the differentiation and function of T lymphocyte subsets in the context of chronic cigarette smoke exposure; and explore the role of PD-L1 in CD103+DCs-mediated Th1/Tc1 cell immunity; finally, investigate the role of IRF8 on the development and function of CD103+DCs and its effect on PD-L1 expression. This study could provide insight into the pathogenesis of smoking-related lung inflammation and emphysema; more important, offer new therapeutic targets for the prevention and treatment of smoking-related COPD.

我们前期研究发现，树突状细胞（DCs）在T淋巴细胞介导的肺部炎症中发挥关键作用。但慢性烟草暴露下，DCs调控T淋巴细胞免疫应答特别是负性调节机制尚未清楚。肿瘤微环境中DCs PD-L1过度表达，诱导T淋巴细胞功能耗竭。据此，我们推测慢性烟草暴露下DCs PD-L1表达下调可能是T淋巴细胞过度活化的重要机制。但在烟草所致慢性炎症状态中，DCs PD-L1的表达情况及调控机制尚未见研究报道。本项目拟系统研究慢性烟草暴露条件下，DCs PD-L1的表达情况与T淋巴细胞亚群分化、功能状态的关系；探讨PD-L1在CD103+DCs介导Th1/Tc1细胞免疫反应中的作用；阐明IRF8对CD103+DCs分化、功能的影响和对PD-L1表达的作用及分子机制。本项目的完成将进一步深入了解慢性烟草暴露下肺部炎症放大及肺结构破坏的发病机制，为吸烟相关慢阻肺的防治提供新的治疗靶点与实验依据。

T淋巴细胞介导的免疫性炎症是烟草相关的肺部慢性炎症的重要机制，而树突状细胞（cDCs）是启动与维持T淋巴细胞免疫反应的关键细胞。已经证实，cDCs功能失调参与肿瘤及许多免疫性疾病的发生发展。但目前对慢性烟草暴露条件下cDCs的表型、功能状态、调控机制仍不是很清楚。因此，针对慢性烟草暴露下cDCs如何调控T淋巴细胞免疫应答的关键科学问题，我们提出慢性烟草暴露下cDCs表现为促炎表型转化，IRF8通过对cDCs分化与功能的调控，同时影响负性分子PD-L1表达，导致过度的Th1与Tc1淋巴细胞免疫反应的科学假说。研究结果显示，慢性烟草烟雾暴露下，肺气肿小鼠肺部存在过度的Th1与Tc1淋巴细胞免疫反应，肺部cDCs向促炎表型转化，表现为高表达共刺激协同分子CD40、CD80、CD86，高分泌促炎因子IL-6、IL-1β、IL-27及IL-12等。同时，模式识别受体（PRRs）RAGE、TLR4的表达水平也显著上调，负性调控分子PD-L1、PD-L2上调，转录因子IRF8、BATF3较IRF4、Blimp-1明显增加。CD103+cDCs亚群与过度的Th1与Tc1淋巴细胞免疫反应相关。IRF8是调控CD103+cDCs亚群分化与促炎表型转化的决定性转录因子。利用IRF8fl/flCD11c(Itgax)-Cre小鼠模型及体外细胞培养证实，IRF8敲除的cDCs分化为CD103+cDCs功能明显减弱，其诱导Th1 和 Tc1分化的功能受到抑制。体外细胞培养显示，特异性阻PD-1/PD-L1分子通路明显促进cDCs诱导的Th1与Tc1淋巴细胞免疫反应。机制研究发现，IRF8通过结合到PD-L1启动子调控PD-L1转录。本研究进一步阐明了烟草相关的肺部慢性炎症的区域免疫重塑及树突状细胞促炎表型转化的相关调控机制，提示针对cDCs的IRF8及PD-L1的调控可能是今后烟草相关肺部慢性炎症抗炎治疗的潜在靶点。