Regulation of T cell maturation

描述（由申请人提供）：成功完成阳性和阴性选择的单个阳性胸腺细胞在获得功能能力并进入长期存活的T细胞库之前，还必须经历最后一步，称为T细胞成熟。最近的胸腺移植物（rte）必须在外周完成T细胞成熟，尽管这一过程知之甚少，部分原因是缺乏在这一发育检查点阻断的小鼠模型，但它既不依赖于通过TCR的抗原特异性信号，也不依赖于通过IL-7R的稳态信号。之前，我们在遗传互补筛选上克隆了转录抑制因子NKAP，以确定T细胞激活的新调节因子。来自CD4-cre NKAP cKO小鼠的T细胞不能经历T细胞成熟。几乎所有外周的幼稚T细胞在表型和功能上都是不成熟的rte。我们使用这个模型来更好地理解T细胞成熟过程中发生的事件。有趣的是，我们发现nkap缺陷的rte不会死于凋亡，而是被补体消除，正如细胞表面的C3沉积所证明的那样。C4和C1q也与nkap缺陷T细胞结合，表明补体途径经典臂的激活。当胸腺细胞在输出到外周之前完成发育时，它们会增加唾液酸在细胞表面与糖蛋白和糖脂的结合。唾液酸的添加是

DESCRIPTION (provided by applicant): Single positive thymocytes that successfully complete positive and negative selection must still undergo one final step, called T cell maturation, before they gain functional competency and enter the long- lived T cell pool. Recent thymic emigrants (RTEs) must complete T cell maturation in the periphery, and although this process is poorly understood, in part due to lack of mouse models blocked at this developmental checkpoint, it is not dependent on either antigen-specific signals through the TCR or homeostatic signals through IL-7R�Previously, we cloned the transcriptional repressor NKAP on a genetic complementation screen to identify novel regulators of T cell activation. T cells from CD4-cre NKAP cKO mice cannot undergo T cell maturation. Almost all naive T cells in the periphery are phenotypically and functionally immature RTEs. We have used this model to better understand the events that occur during T cell maturation. Interestingly, we find that NKAP-deficient RTEs do not die by apoptosis, but rather are eliminated by complement, as demonstrated by C3 deposition on the cell surface. C4 and C1q are also bound to NKAP-deficient T cells, indicating activation of the classical arm of the complement pathway. As thymocytes complete development before export to the periphery, they increase incorporation of sialic acid into glycoproteins and glycolipids at the cell surface. This addition of sialic acid is critical to lymphocyte survival in the periphery, as stripping of cell surface sialic acids by neuraminidase leads to the binding of natural IgM and complement fixation. We find that NKAP-deficient T cells have a defect in sialylation, as demonstrated by increased binding of peanut agglutinin (PNA), leading to IgM recruitment. As T cells mature, they also upregulate expression of the complement inhibitor DAF/CD55 on the cell surface, but this is defective in NKAP-deficient RTEs which exacerbates complement-mediated elimination. Specifically, we find that the incorporation of �8-linked sialic acids occurs concurrently with T cell maturation, and that this is altered in the absence of NKAP. There are six related proteins that mediate �8 sialylation, and we find that one of them, ST8Sia6, is turned on specifically with maturation and that its expression is decreased in the absence of NKAP. Our preliminary results demonstrate that one substrate of ST8Sia is CD45, where it controls CD45 function through regulating dimerization, and therefore may regulate T cell responsiveness during T cell maturation. We believe that NKAP may work with Hdac3 and Runx1 to regulate T cell maturation, because CD4-cre knockout of either gene results in a phenotype similar to the NKAP knockout with respect to IgM/complement deposition, decreased �8 sialylation and CD55 expression, which will be explored in this proposal.