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稳态显然很重要，但令人惊讶的是，人们对所涉及的细胞内信号传导途径知之甚少。为此，我们鉴定出了 DRAK2，一种在淋巴组织中高度富集的丝氨酸/苏氨酸激酶。作为 DAP 激酶家族的成员，DRAK2 在某些细胞系中异位表达时可诱导细胞凋亡。在 DRAK2 工程缺陷小鼠中，T 淋巴细胞发育和激活中的许多重要缺陷是显而易见的。来自这些小鼠的 T 细胞在 T 细胞受体的刺激下过度增殖，表明该激酶在 T 细胞静止中发挥着意想不到的作用。与这一发现一致，DRAK2-/- 小鼠的活化 T 细胞比例增加 外周淋巴器官中的细胞。此外，DRAK2缺陷的T细胞在缺乏T细胞激活通常所需的共刺激信号的情况下增殖。我们发现，野生型 T 细胞需要 T 细胞受体 (TCR) 和 CD28 交联来实现快速且持续的钙反应，而 DRAK2 缺陷型 T 细胞仅需要通过 TCR 进行刺激。矛盾的是，在 DRAK2 缺陷的 T 细胞中，超抗原暴露后的克隆扩增存在显着缺陷。这种对超抗原的反应缺陷是由于激活诱导细胞死亡（AICD）增强所致。我们很好奇 DRAK2 干扰 T 细胞激活的机制以及其活性如何调节免疫耐受。我们将确定 DRAK2-/- 小鼠中已知的 T 细胞激活途径是否有缺陷。我们将从生化角度表征激酶以确定其作用模式。最后，我们将评估当 AICD 被阻止时它缺失的后果。这些结果旨在更全面地了解 T 细胞激活的负调节，以及这种负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.