IRF8在结核病患者MAIT细胞免疫功能异常中的作用及机制

MAIT cells are newly identified innate T cells that play critical role in protective immunity against infection. In our previous studies, we found that the frequency of MAIT cells was significantly reduced both in peripheral blood from patients with active pulmonary TB and in tuberculous pleural effusions compared with healthy controls. When MAIT cells were stimulated with E. coli, patients with active TB had significantly lower production of IFN-γ and TNF-α compared with healthy controls, suggesting functional defect of MAIT cells in patients with TB. To understand molecular mechanisms of the functional defect, we performed RNA-seq on sorted MAIT cells from patients with active TB and healthy controls. IRF8 was one of genes that showed most significant difference between the two groups. Our hypothesis is that IRF8 plays a critical role in the regulation of MAIT cell differentiation and functions, and is associated with functional defect of MAIT cells from patients with TB. The role of IRF8 in MAIT cells is still largely unknown. In this application, we plan to investigate the role of IRF8 in regulating differentiation and effector molecule production of MAIT cells from healthy controls and patients with TB, and the association of expression level of IRF8 with disease progress and outcome; to study the regulating mechanisms of IRF8 expression in MAIT cells by antigens of Mycobacterium tuberculosis. The study has an important impact on understanding mechanisms of anti-TB immunity by MAIT cells.

MAIT细胞是一类新发现的固有免疫样T细胞，在抗感染免疫中发挥重要作用。我们前期研究发现，在结核病患者外周血及结核性胸膜炎胸腔积液中MAIT细胞比例显著降低，且伴随IFN-γ和TNF-α产生降低等功能异常。为了解MAIT功能异常的分子机制，我们对结核病患者和正常对照者MAIT细胞进行了转录组测序，发现IRF8在结核病患者MAIT细胞表达显著降低。我们的假说是：IRF8在MAIT细胞分化及功能中起了重要的调节作用，是MAIT细胞抗结核免疫的关键调控因子，结核病患者MAIT细胞功能异常与IRF8密切相关。到目前为止，IRF8在MAIT细胞分化及功能中的调控作用尚未见报道。我们计划研究IRF8在MAIT细胞分化及效应分子产生中的调节作用，及与结核病发病及转归的关系；研究结核分枝杆菌在调节MAIT细胞IRF8表达中的作用及分子机制。该研究对了解MAIT细胞抗结核免疫的机制有非常重要的意义。

黏膜相关恒定T细胞（mucosal-associated invariant T cells, MAIT cells）是一类新发现的固有免疫样T细胞，在抗感染免疫中发挥重要作用，但其在活动性结核病患者中的作用尚有待深入研究。我们研究了结核性胸膜炎患者胸腔积液MAIT细胞和外周血MAIT细胞的表型及功能，发现结核性胸腔积液MAIT细胞IFN-γ、IL-17F和颗粒酶B的表达显著高于外周血MAIT细胞；结核性胸腔积液MAIT细胞IFN-γ产生与结核病病变范围及严重程度密切相关。我们对IRF8在MAIT细胞抗结核免疫中的作用进行了研究，发现结核性胸膜炎患者胸腔积液MAIT细胞在结核分枝杆菌抗原刺激前表达较低，在结核抗原过夜刺激后表达显著增高。对正常对照者和结核病患者外周血MAIT细胞及结核性胸膜炎患者胸腔积液MAIT细胞IRF8表达的研究发现，经结核分枝杆菌抗原刺激后，结核性胸膜炎患者胸腔积液MAIT细胞IRF8表达显著高于结核病患者和正常对照者外周血MAIT细胞。为了研究IRF8对MAIT细胞免疫功能的调节作用，我们比较了IRF8阳性和阴性MAIT细胞IFN-γ和granzyme B的产生情况，发现IRF8+ MAIT细胞IFN-γ产生显著高于IRF8- MAIT细胞，但granzyme B的产生未发现存在显著差异。该研究结果提示IRF8可能参与了MAIT细胞IFN-γ免疫功能的调节。进一步研究了IRF8在MAIT细胞免疫功能及分化中的作用，发现IRF8+ MAIT细胞CD25、CD69、CD132和CD137表达均显著高于IRF8- MAIT细胞，提示IRF8+ MAIT细胞呈现激活表型。IRF8+ MAIT细胞CD62L和CCR7的表达也显著增高，提示IRF8与MAIT细胞分化为记忆细胞相关。为了研究IRF8对共刺激受体的调节作用，我们比较了PD-1、LAG-3、BTLA的表达水平，发现IRF8+ MAIT细胞PD-1、LAG-3和BTLA表达显著高于IRF8- MAIT细胞，提示IRF8可能通过调节共刺激分子表达参与MAIT细胞免疫调节。我们进一步研究了IRF8调控T-bet、EOMES等的机制。该研究对了解抗结核免疫保护机制有比较重要的意义。