Cytokine signaling in developing thymocytes and T cells

关于T细胞发育的传统观点认为，来自同一T细胞受体（TCR）的信号决定了阳性和阴性选择以及成熟CD4+辅助细胞和CD8+细胞毒性细胞的谱系选择。这是如何实现的确切机制仍然存在争议，但有人提出，TCR信号的定量或定性差异可以解释谱系选择的不同结果。与这些观点相反，本研究表明TCR信号本身不足以决定发育中的胸腺细胞的细胞命运，CD4/CD8谱系选择需要细胞因子如白素-7 （IL-7）的额外提示。通过条件删除IL-7受体的直接下游信号分子，我们证明了IL-7诱导的细胞因子信号是CD8谱系选择和体内成熟CD8+细胞毒性T细胞分化所必需的。我们的数据证实了体内IL-7和其他γ -c细胞因子在未成熟胸腺细胞的CD8谱系承诺中的作用，这与T细胞谱系选择的动力学信号模型是一致的。我们最近还发现了非γ c-细胞因子（IL-6， TSLP和IFNgamma）在CD8谱系承诺中的意想不到的作用，并正在积极分析它们在胸腺阳性选择中的作用模式。

The conventional view on T cell development posits that signals from the same T cell receptor (TCR) determines both positive and negative selection as well as lineage choice into mature CD4+ helper and CD8+ cytotoxic cells. The precise mechanism how this is achieved is still under dispute but it has been proposed that either quantitative or qualitative differences in TCR signaling would account for the different outcomes of lineage choice. In contrast to such views, here we show that TCR signaling alone is not sufficient to determine cell fate of developing thymocytes, and that CD4/CD8 lineage choice requires additional cues by cytokines such as interleukin-7 (IL-7). Using conditional deletion of immediate downstream signaling molecules of the IL-7 receptor, we demonstrate that IL-7 induced cytokine signals are required for CD8 lineage choice and for the differentiation into mature CD8+ cytotoxic T cells in vivo. Our data establish a previously unappreciated role for in vivo IL-7 and other gamma c-cytokines in CD8 lineage commitment of immature thymocytes, which is consistent with the kinetic signaling model of T cell lineage choice. We have recently also identified an unexpected role for non-gamma c-cytokines (IL-6, TSLP, and IFNgamma) in CD8 lineage commitment and are actively analyzing their mode of action during positive selection in the thymus.