【作者】 吕俊；

【导师】 鲁林荣；

【作者基本信息】 浙江大学 ， 免疫学， 2019， 博士

【摘要】 T细胞在胸腺中发育成熟。在顺利完成VDJ重排并发育到双阳性(Double Positive,DP)阶段后,细胞表面表达的T细胞受体(TCR)必须要与胸腺皮质细胞表面MHC-多肽结合,才能进一步继续发育成CD4+T细胞和CD8+T细胞,这一过程被称为阳性选择,TCR结合抗原向胞内传递足够的存活信号是阳性选择的关键。与成熟的外周T细胞不同,DP胸腺T细胞内TCR信号的激活面临两个特殊的困难:一是在其细胞表面TCR分子尚未充分上调,其次是需要对低亲和力自身肽-MHC分子复合物做出响应。因此,DP胸腺T细胞的TCR信号传导需要比外周T细胞更加敏感高效。一般认为,胸腺T细胞可以表达一些特殊的信号分子来增强TCR信号,从而促进阳性选择,但是迄今为止,科学家们并没有发现只特异性调控胸腺T细胞TCR信号传导的分子。Themis和Tespa1是两个近年来新定义的蛋白,它们对优化TCR信号及T细胞发育至关重要。它们的缺陷会导致表型类似的T细胞阳性选择受损。本研究中,我们系统地比较了这两个分子对阳性选择的影响。我们发现,Tespa1缺失会对阳性选择中T细胞的基因表达谱产生更局限且特异的影响。在骨髓嵌合小鼠中,我们发现,Tespa1-/-T细胞体现出比Themis-/-T细胞更为严重的发育损伤。然而,在阳性选择完成之后,Tespa1-/-T细胞体现出较强的稳态增殖能力,并且逐渐在外周淋巴器官中占有更高的比例。这些证据提示Tespa1是一个胸腺特异的TCR信号调节蛋白。我们接着通过构建Tespa1条件性敲除小鼠验证这一猜想,结果发现Tespa1在外周T细胞中的敲除并不影响TCR信号及细胞的增殖。我们还在研究中构建了 Tespa1及Themis双敲除(DKO)小鼠,发现DKO小鼠导致了胸腺T细胞发育缺陷的叠加,进一步证明了 Tespa1与Themis通过相互独立的机制调节胸腺细胞阳性选择。更多还原

【Abstract】 Double positive(DP)thymocytes undergo positive selection to become mature CD4+or CD8 single positive T cells under the instruction of T-cell receptor(TCR)signal.Unlike mature T-cells,DP cells are required to respond to low affinity self-peptide-MHC ligands before full upregulation of their surface TCR expression.Thus,DP thymocytes nust be more sensitive to ligand than mature T-cells.A number of molecules have been found to be able to augment the strength of the TCR signal to facilitate positive selection.However,almost all of them are also active in mature T-cells.Themis(thymocyte-expressed molecule involved in selection)and Tespal(thymocyte-expressed positive selection associated 1),are two newly defined molecules essential for optimal TCR signaling and thymocyte development.The deficiency of either molecule leads to defects in positive selection.Here we compared their relative contributions in thymocytes during positive selection.We show that Tespal deficiency led to more confined and specific gene expression profile changes in cells undergoing positive selection.In mixed bone manrow transfer experiments,Tespa1-/-cells displayed more severe defects in thymocyte development than Themis-/-cells.However,Tespa1-/-cells exerted a substantial degree of homeostatic expansion and became dominant in peripheral lymphoid organs,suggesting Tespa1 is a thymic-specific TCR signaling regulator.This hypothesis is further supported by our observations in Tespal conditional knockout mice,as Tespal deletion in peripheral T-cells didn’t affect TCR signaling and cell proliferation.The differential regulatory roles of Tespal and Themis is in accordance with their nonredundant roles in thymocyte selection,wherein Tespa1 and Themis double knockouts showed additive defects.更多还原