支链氨基酸调节抗结核多能T细胞免疫应答的模式及相关机制研究

It is widely accepted that polyfunctional T cells with the capacity to produce multiple cytokines, such as IL-2, TNF-α and IFNγ, play key roles in the protection against tuberculosis. Our preliminary data indicated that the frequency of Mycobacterium tuberculosis (Mtb)-specific polyfunctional T cells in the periphery of tuberculosis patients complicated by type 2 diabetes mellitus (TB+DM) was much lower than that in tuberculosis patients (TB). Meanwhile, the peripheral branched-chain amino acids (BCAA) levels in TB+DM patients also decreased in parallel. It is reported that BCAA modulates the activation and differentiation of T cells via binding to the system L amino acid transporter 1 (LAT1/SLC7A5) located on cell membrane. Loss of LAT1/SLC7A5 leads to the impaired uptake of BCAA and abnormal T cell metabolic reprogramming to glycolysis, which is necessary for T cell activation and differentiation. To date, whether and how BCAA is engaged in modulating M.tb-specific T cell responses is still unclear. Here we propose that the decreased level of peripheral BCAA in TB+DM patients might be one of the key factors that mediate the aberrant differentiation of M.tb-specific polyfunctional T cells and alter the T cell immune response patterns. In this project, by using immunological and metabolic methods, we intend to investigate the relevance between the expression of BCAA membrane transporter LAT1 and the distribution and function of M.tb-specific polyfunctional T cells in TB+DM patients. We will further reveal the modulating patterns of M.tb-specific T cell responses by BCAA and elucidate the relevant molecular mechanisms. Our study will provide direct evidence on the importance of BCAA supplementation to TB patients complicated with diabetes.

多功能T细胞被认为具有更好的抗结核免疫功能。我们前期同步比较单纯结核病(TB)与结核合并糖尿病(TB+DM)患者的代谢组学和免疫学特征时，发现TB+DM组外周抗结核多能T细胞的数量和分泌细胞因子的水平明显低于TB组，同时TB+DM组外周支链氨基酸(BCAA)的水平也低于TB组。研究表明BCAA通过T细胞表面的LAT1受体参与T细胞的活化和分化。该受体缺陷抑制T细胞向活化所必需的糖酵解模式转化，进而阻碍T细胞功能性分化。本项目以“BCAA调节多能T细胞免疫应答模式”为研究对象，提出“TB+DM患者中BCAA水平低可能影响抗结核多能T细胞分化和功能”的科学假设，利用TB+DM临床样本，分析抗结核特异性T细胞表面LAT1的表达和BCAA调节抗结核多能T细胞免疫应答的模式，获得TB+DM患者中抗结核多能T细胞数量和功能异常的分子机制，为BCAA作为结核合并糖尿病治疗中新的辅助手段提供理论基础。

本项目围绕支链氨基酸（BCAA）参与调节抗结核感染T细胞免疫应答的模式和机制开展了系列研究。本项目执行期间，获得不同患者抗结核特异性T细胞的亚群表型及功能，初步明确了与结核病（TB）患者相比，结核合并糖尿病（TBDM）患者外周抗结核特异性T细胞功能存在缺陷，且与细胞活化水平无明显关系。分析比较不同人群外周免疫细胞功能，细胞内不同能量代谢相关基因和代谢小分子的转运载体，结果发现BCAA对不同患者外周抗结核特异性T细胞功能的差异可能与氨基酸转运载体的表达水平有关。进一步分析比较发现，BCAA可能参与细胞能量代谢，但是主要体现在T细胞糖酵解能力的改变。此外，我们通过分析比较结核病随访患者，获得抗结核治疗进程中外周免疫组学和代谢组学特征谱。本项目开展至今所得结果为阐述BCAA调节抗结核特异性T细胞功能免疫应答的机制提供了一定量的数据积累，后期将继续完成相关工作，进一步明确和解析其中的机制。