幼年小鼠CD4+胸腺迁出细胞的肝脏耐受机制研究

Mechanisms of peripheral tolerance play a critical role in preventing T cells that escape from negative selection in the thymus from initiating autoimmune reactions. Compared to the adult mice, the number, phenotype and function of peripheral T cells as well as the microenvironment of peripheral lymphoid-organs in the infant mice are different, suggesting that there might be differences in the mechanisms of peripheral tolerance of T cells between the infants and the adults. We have previously found that in the adult mice, a subset of autoreactive CD4+ recent thymic emigrants (RTEs) was retained in the liver after their emigration from the thymus, and acquired tolerance there. However, in the infant mice, the peripheral tolerance of T cells, especially that of RTEs that have just emigrate from the thymus remain poorly understood. In this project, we intend to investigate the mechanisms of peripheral tolerance of CD4+ RTEs in the infant mice. Also, we want to explore the significance of liver tolerance of CD4+ RTEs in establishing and maintaining the immune tolerance during infancy. The results will help us better understand the peripheral tolerance of T cells in the infancy, and provide new prospect for the mechanisms and treatment of relative autoimmune diseases.

逃离胸腺中枢耐受的自身反应性T细胞需要外周耐受的调控，避免对机体造成损伤。外周耐受机制的缺陷会导致自身免疫病的发生。幼年与成年时期相比，外周T细胞的数量、表型和功能存在差异，外周淋巴器官的微环境也存在差异，提示幼年可能有与成年不同的T细胞外周耐受机制。我们的前期研究发现成年小鼠中一群高自身反应性CD4+胸腺迁出细胞（RTE）输出胸腺后倾向于在肝脏滞留，并通过多种机制完成在肝脏中的耐受。然而幼年时期T细胞的外周耐受机制、尤其是刚输出胸腺的RTE如何发生外周耐受还不清楚。本项目拟对幼年小鼠CD4+RTE在外周、尤其是在肝脏的耐受机制进行研究，比较其与成年鼠耐受机制的差异，并进一步探讨幼年RTE的肝脏耐受对于幼年时期免疫耐受建立和维持的意义。研究结果将为全面了解幼年时期T细胞的外周耐受机制提供新的视角，并为幼年阶段相关自身免疫病的发病机制和治疗手段提供新的思路。

新生及幼年时期T细胞的外周耐受调控对于机体免疫稳态的建立和维持至关重要，耐受调控缺陷可能会导致自身免疫性疾病的发生。本项目研究了新生及幼年时期CD4+胸腺迁出细胞（recent thymic emigrants, RTE）的肝脏耐受调控。研究发现新生及幼年时期CD4+RTE中Foxp3-Tconv细胞在肝脏中呈现活化表型，上调耐受相关分子的表达和凋亡水平，并分泌更多抑制性细胞因子IL-10。研究还发现新生及幼年时期CD4+Foxp3+Treg细胞在肝脏中阶段性聚集，清除Treg细胞、抑制肝脏的阶段性聚集会导致肝脏出现Th1型炎症反应及代谢紊乱。与脾脏Treg细胞相比，肝脏CD4+RTE中Foxp3+Treg细胞含有更多活化型Treg，增殖、凋亡水平比脾脏高，稳定性也比脾脏高，表型和功能均与脾脏Treg存在差异。新生及幼年时期肝脏Treg的活化依赖MHC II类分子所呈递的抗原，但不依赖于自身免疫调节因子（Autoimmune regulator, Aire）调控的抗原表达。在自身免疫性肝损伤模型中，我们同时筛选到调控CD4+T细胞功能缓解肝损伤的天然多糖产物Salecan。本项目综合利用不同的实验技术和研究体系，在动物、细胞和分子水平揭示了新生及幼年时期不同亚群CD4+RTE在肝脏中的调控过程，为调控缺陷导致的相关疾病的机制研究和治疗提供理论依据。