Modulation of T Cell Activation and Tolerance by DRAK2

尽管免疫耐受对于预防自身免疫和维持淋巴细胞内稳态很重要，但令人惊讶的是，人们对其中涉及的细胞内信号通路知之甚少。为此，我们鉴定了DRAK2，一种在淋巴组织中高度丰富的丝氨酸/苏氨酸激酶。作为DAP家族中的一员，DRAK2在某些细胞系中异位表达时可诱导细胞凋亡。在DRAK2基因工程缺陷的小鼠中，T淋巴细胞发育和激活的一些重要缺陷是明显的。来自这些小鼠的T细胞通过T细胞受体过度增殖到不理想的刺激，这表明在T细胞对这种激酶的静止中发挥了意想不到的作用。与这一发现一致的是，DRAK2-/-小鼠激活的T细胞比例增加 外周淋巴器官中的细胞。此外，DRAK2缺陷的T细胞在没有共刺激信号的情况下增殖，这通常是T细胞激活所必需的。我们已经发现，野生型T细胞需要T细胞受体(TCR)和CD28的交联来快速和持续的钙反应，而DRAK2缺陷的T细胞只需要通过TCR来刺激。矛盾的是，超抗原暴露后的克隆性增殖在DRAK2缺陷的T细胞中是显著缺陷的。这种对超抗原的缺陷反应是由于增强了激活诱导的细胞死亡(AICD)。我们对DRAK2干扰T细胞活化的机制以及它的活性如何调节免疫耐受很感兴趣。我们将确定已知的T细胞激活通路在DRAK2-/-小鼠中是否存在缺陷。我们将从生物化学的角度来描述该激酶，以确定其作用模式。最后，我们将评估当AICD被阻止时没有它的后果。这些结果旨在更深入地了解T细胞激活的负性调节，以及这种负性调节如何促进免疫耐受。

Although immune tolerance is clearly important for the prevention of autoimmunity and the maintenance of lymphocyte homeostasis, suprisingly little is known about the intracellular signaling pathways that are involved. To this end, we have identified DRAK2, a serine/threonine kinase that is highly enriched in lymphoid tissues. As a member of the DAP family of kinases, DRAK2 induces apoptosis upon ectopic expression in certain cell lines. In mice with an engineered deficiency in DRAK2, a number of important defects in T lymphocyte development and activation are apparent. T cells derived from these mice are hyperproliferative to suboptimal stimulation through the T cell receptor, indicating an unexpected role in T cell quiescence for this kinase. In accord with this finding, DRAK2-/- mice have an increased proportion of activated T cells in peripheral lymphoid organs. Furthermore, DRAK2-deficient T cells proliferate in the absence of costimulatory signals normally required for T cell activation. We have found that whereas wildtype T cells require crosslinking of both the T cell receptor (TCR) and CD28 for a rapid and sustained calcium response, DRAK2-deficient T cells require only stimulation via the TCR. Paradoxically, clonal expansion following superantigen exposure is dramatically defective in DRAK2-deficient T cells. This defective responsiveness to superantigen is due to enhanced activation-induced cell death (AICD). We are curious about the mechanisms by which DRAK2 interferes with T cell activation and how its activity may modulate immune tolerance. We will determine if known T cell activation pathways are defective in DRAK2-/- mice. We will characterize the kinase biochemically to determine its mode of action. Finally, we will assess the consequences of its absence when AICD is blocked. These results are aimed at providing a more thorough understanding of negative regulation of T cell activation, and how such negative regulation contributes to immune tolerance.