肠道共生菌促进肝脏γδT-17细胞发育分化的机制研究

IL-17 secreted γδT cell is also known as γδT-17 cell, the past researches about γδT-17 cell mostly focused on the mucosa immune system including lung, intestine and skin, but few studies pay attention to γδT-17 cells in the liver who contain abundant γδT cells and is constantly stimulated by the microbiota product from the intestine. Our pre-experiment found that mouse liver was rich of γδT-17 cells, additionally its frequency decreased significantly after microbiota depleted. This study will systematically demonstrate and deeply uncover the mechanism of microbiota in promoting the differentiation of hepatic γδT-17 cell. Firstly, we will detect the characteristics of the normal mice hepatic γδT-17 cells, including cytokines, phenotype and transcription factor. Secondly, the change of the characteristics and the function of hepatic γδT-17 cells will be assayed when the microbiota were depleted and rebuilt. Finally, based on the hepatic virus infection model, the molecular mechanism and the clinical significance of microbiota in promoting hepatic γδT-17 differentiation will be further resolved from three aspects, including cytokines signal, TLR signal and antigen signal, the reason why liver uniquely contain abundant γδT-17 cells (but not IFN-secreted γδT cell subtype) will also be determined. This study will interpret the correlation between microbiota and hepatic γδT-17 cells, providing new theoretical basis for the study of the intestine-liver immune crosstalk.

分泌IL-17的γδT细胞也称γδT-17细胞，以往γδT-17细胞的研究多集中在肺脏、肠道和皮肤等粘膜免疫系统，而肝脏γδT-17细胞则鲜有报道。我们预实验首次发现小鼠肝脏富含γδT-17细胞，在肠道共生菌清除后则显著降低。本研究拟系统证实并深入解析肠道共生菌在肝脏γδT-17细胞分化驻留过程中的作用及其机制。我们将检测正常小鼠肝脏γδT-17细胞的基本特性（细胞因子、细胞表型和转录因子等）；观察共生菌清除与重建状态下小鼠肝脏γδT-17细胞的特性与功能变化；最终采用肝脏病毒感染小鼠模型，从细胞因子信号、TLR信号和抗原信号三个角度进一步解析共生菌促进肝脏γδT-17细胞发育分化的机制及其在肝脏疾病的意义，确认肝脏特殊富含γδT-17细胞亚群（而不是分泌IFN-γ的γδT细胞亚群）的原因。本研究将阐释共生菌与肝脏γδT-17细胞之间的作用关系，为肠-肝免疫交互作用的研究提供新的理论依据。

共生菌可以通过多种多样的机制维持机体区域免疫稳态，其中包括诱导和维持肠道、皮肤、腹腔和肺脏局部的IL-17A分泌型γδT细胞（γδT-17细胞）。肝脏因为其独特的血液循环位置可以持续接收来自肠道微的微生物代谢产物刺激，但是对肝脏γδT细胞的组成及其与共生菌关系的研究还非常匮乏。我们的研究表明肝脏γδT细胞具有肝脏驻流特性并且以分泌IL-17A为主，而共生菌可以通过促进肝脏γδT-17细胞活化、存活和增殖来维持肝脏γδT-17细胞的稳态。进一步的研究表明整体共生菌的数量决定着肝脏γδT-17细胞的数量，单一类型的大肠杆菌重建即可以剂量依赖性的方式促进肝脏γδT-17细胞的形成。分子机制研究表明肝实质细胞通过CD1d呈递共生菌来源的磷脂类抗原维持肝脏γδT-17细胞的稳态，且该过程不依赖于TLR受体信号或者IL-1/IL-23受体信号。小鼠体内外实验均表明补充外源性共生菌可以显著促进肝脏γδT-17细胞的数量。更重要的是，共生菌通过促进γδT-17细胞加剧非酒精性脂肪性肝病的发生发展。总之，我们的研究表明肠道共生菌通过肝脏实质细胞CD1d/磷脂类抗原的途径维持肝脏驻留性γδT-17的稳态。