mTOR和TGFβ信号通路调控DETCs诱导T细胞分化在皮肤移植排斥反应中的作用及机理研究

The traditional view of skin transplantation is that langerhan cells (LC) is critical for skin allograft rejection, because it carry allograft antigen to activate recipient na?ve T cells in peripheral lymph nodes. However, current data demonstrated that only LCs were not enough to cause allograft skin rejection. Dendritic epidermal T cells (DETCs) are T lymphocytes that express a canonical TCR γδ and form a dense network in skin. Our preliminary datas showed that activated DETCs refractorily produced high level of IFNγ and could directly induce naive CD4 T cells to differentiate to Th1 cells and promote skin allograft rejection.However, treated with rapamycin and TGFβ, DETCs significantly down-regulated expression of IFN gamma and up-regulated expression of Foxp3 and TGFβ, and induced na?ve CD4 T cells to differentiate to Treg cells and inhibited skin allograft rejection.Accordingly, we here will provide and testify the hypothesis: Both mTORC2-Akt-FoxO and TGFβ-smad signal transduction pathway regulate expression of the key transcription factors T-bet and Foxp3; T-bet promotes production of IFN gamms, wheras, Foxp3 enhances the expression of TGFβ; Then, IFNgamma+ DETCs induced na?ve T cells to differentiate to Th1 cells, which promote allograft rejection; TGFbeta+ DETCs induced na?ve T cells to differentiate to Treg cells, which inhibit allograt rejection.

表皮内γδT细胞（DETCs）是皮肤免疫系统中的重要细胞并参与皮肤移植排斥反应。我们前期研究首次发现：①.DETCs具有专职递呈细胞的功能，其激活后自发性高表达IFNγ并诱导Th1细胞产生，过继到受体小鼠能加速排斥反应；②.经雷帕霉素和TGFβ共培养后，DETCs显著下调IFNγ/上调Foxp3和TGFβ的表达并诱导Treg产生，过继到受体小鼠能抑制排斥反应；但雷帕霉素或TGFβ单独培养则无此效应。提示mTOR与TGFβ信号通路在DETCs调节皮肤排斥反应中起重要作用。而FoxO和Smad是调控T细胞分化关键转录因子Foxp3/T-bet产生的重要分子。因此，本课题拟在前期基础上提出并验证假说：mTORC2-Akt-FoxO和TGFβ-smad信号通路通过调控DETCs转录因子T-bet/Foxp3表达来调节细胞因子IFNγ和TGFβ的产生，从而影响T细胞分化方向以调节皮肤移植免疫反应。

皮肤组织中的γδ T细胞主要由Vγ1、Vγ4、Vγ5三种功能不同的亚群组成。其中Vγ5亚群（DETCs）分布于表皮组织，主要通过分泌IGF-1/KGF-1促进创面愈合。Vγ1和Vγ4 亚群则分布于淋巴结、脾脏、外周循环以及真皮组织中。Vγ1和Vγ4 T细胞激活后可产生大量的IFN-γ或IL-17，从而在免疫移植排斥反应、感染免疫以及抗肿瘤免疫中起重要作用。我们发现在皮肤移植早期，真皮内及外周循环浸润到移植局部皮肤组织中的γδ T细胞在皮肤组织分泌的IL-1β/23作用下，形成IL-1β/23-IL-17轴引发的移植皮肤局部炎症级联放大效应。从而促进皮肤移植物中的DCs成熟并迁入受体皮肤引流淋巴结，增强抗原特异性naive T细胞激活效应，最终导致皮肤移植物加速排斥。另外，我们发现在创缘表皮组织中，DETCs与角朊细胞形成的IGF-1-IL-15正反馈环路以及Vγ4 T细胞与与角朊细胞形成的IGF-1-IL-15正反馈环路，分别通过增强创面再上皮化过程及局部炎症协同促进糖尿病创面愈合。这些研究结果表明以γδ T细胞为主导的皮肤免疫在异基因皮肤移植排斥反应及创面愈合过程中起关键作用。