GENE REGULATORY EVENTS IN ESTABLISHING MATURE T CELL TOLERANCE

现代免疫学的基本问题之一是控制CD4+辅助T细胞分化为具有离散效应功能的亚群。特别令人感兴趣的是这些亚群如何相互作用，以促进强大的免疫力和终身稳定的免疫耐受。各种研究表明，目前至少有五个定义明确的亚集：Th0、Th1、Th2、Treg和Th17既能促进彼此的行为，也能抑制对方的行为。最近，大量的实验关注于高水平表达有翼叉头转录因子FoxP3的CD4+，CD25+T细胞亚群。这一亚群严格限制他们自己表达增殖性细胞因子，通常不能产生IL-2和IL-4等生长细胞因子。这些细胞已被证明削弱了其他常规的CD4+T细胞的激活，这在自身免疫反应中可能是重要的；因此，这些细胞被称为T调节(Treg)细胞。尽管进行了大量的研究，但仍不清楚Treg细胞通过什么分子机制能够抑制T细胞的其他亚群，以及它们在正常免疫反应中扮演什么角色。为了研究Tregs抑制效应的分子基础，我们研究了一种共培养系统，在该系统中，Tregs被用来抑制传统的CD4T细胞对T细胞受体激动剂的反应。我们发现，1：1的混合细胞可以观察到有效的抑制作用。在此条件下，我们观察到常规T细胞发生了凋亡。此外，我们发现目前流行的抑制IL-2基因转录的模型是不正确的。反应细胞的死亡可以定量地解释T细胞反应的丧失。我们发现，各种常见的伽马链细胞因子能够完全逆转由于Treg抑制而导致的死亡。这似乎是由于Tregs消耗但不能产生细胞因子，从而剥夺了传统T细胞的细胞因子。结合这些实验，我们发现Bim基因的缺陷完全将T细胞从Treg抑制中拯救出来。我们还证明，在炎症性肠病模型中，体内也可以观察到类似的细胞凋亡和T细胞缺失效应。综上所述，这些数据表明Treg细胞通过多克隆缺失的形式发挥其抑制作用，而不是抑制应答的常规T细胞中的细胞因子转录。我们的观察为这一T细胞亚群提供了新的线索，我们现在正试图开发一个T细胞亚群如何实现耐受和免疫的一般模型。这些研究可能对自身免疫性疾病、传染病和肿瘤免疫具有重要意义。

One of the fundamental questions of modern immunology is the control of CD4+ helper T-cell differentiation into subsets with discrete effector functions. Of special interest is how the subsets interact with each other to promote strong immunity and lifelong stable immunological tolerance. A variety of investigations show that there are at this time at least five well-defined subsets: Th0, Th1, Th2, Treg, and Th17 that can both promote and inhibit the behavior of each other. Recently, a great deal of experimental attention has been directed at the subset of CD4+,CD25+ T cells that express high levels of the winged fork head transcription factor, FoxP3. This subset strictly limits their own expression of proliferative cytokines and is generally incapable of producing growth cytokines such as IL-2 and IL-4. These cells have been shown to impair the activation of other conventional CD4+ T cells which could be important during autoimmune reactions; hence these cells are called T regulatory (Treg) cells. Despite a great deal of investigation, it is still unclear by what molecular mechanisms Treg cells are capable of suppressing other subsets of T cells and what role they play in normal immune reactions. In order to examine the molecular basis of the suppressive effects of Tregs, we investigated a co-cultivation system in which Tregs were used to suppress conventional CD4 T cells responding to T cell receptor agonists. We found that potent suppression could be observed with 1:1 mix of cells. Under these conditions, we observed that the conventional T cells underwent apoptosis. Furthermore, we found that the prevailing model of suppression of IL-2 gene transcription was incorrect. Death of the responding cells could quantitatively account for the loss of T cell response. We found that various common gamma chain cytokines were able to completely reverse the death due to Treg suppression. This appeared to be due to the fact that Tregs consumed, but could not produce, the cytokines and thereby deprived the conventional T cells of cytokines. In conjunction with these experiments, we found that a deficiency of the Bim gene completely rescued T cells from Treg suppression. We also demonstrated that similar apoptosis and T cell deletion effects could be observed in vivo in an inflammatory bowel disease model. Taken together, these data suggest that Treg cells exert their suppressive effect by a form of polyclonal deletion rather than suppression of cytokine transcription in the responding conventional T cells. Our observations shed new light on this subset of T cells and we are now attempting to develop a general model of how T cell subsets achieve tolerance and immunity. These investigations may have importance for autoimmune disorders, infectious diseases, and tumor immunity.