Molecular mechanisms of Th17 plasticity in MS

描述(申请人提供)：多发性硬化症(MS)及其小鼠模型(实验性自身免疫性脑脊髓炎；EAE)是由自身反应性CD4+T细胞发起和传播的中枢神经系统自身免疫性疾病。CD4+T细胞的两个亚群Th1和Th17与自身免疫性疾病尤其是MS的发病有关，然而，髓鞘特异性Th1和Th17细胞在中枢神经系统(CNS)自身免疫中的相对作用仍存在争议，因为无论是IL-17F、IL-17A还是干扰素-g缺陷小鼠都不能完全保护CNS自身免疫的发生。相比之下，IL-23p19和IL-23受体(IL-23R)缺陷小鼠对EAE的发生具有高度的抵抗力。此外，在自身免疫性疾病患者的炎症组织中，已发现大量共表达干扰素-g和白介素17的Th细胞。在自身免疫过程中，它们在靶组织中的频率增加，表明这些细胞在疾病过程中发挥着重要作用。然而，这些细胞在自身免疫中的起源、稳定性和功能仍然是个谜。我们已经确定，大多数中枢神经系统浸润性T细胞在EAE过程中表达IL-23R，而与其产生的细胞因子(IL-17和/或干扰素-g)无关，因为它们来自Th17细胞。我们进一步证明，IL-23在Th17可塑性中起关键作用，因为它促进了Th17细胞中IL-17+干扰素-g+T细胞(Th17/g)的产生。尽管Th17/g细胞表达T-bet，但这些细胞中的干扰素-g的产生不受T-bet或其他干扰素-g促进转录因子的控制。相反，我们发现AhR是一个关键的转录因子，推动Th17细胞对IL-23的反应产生干扰素-g。我们还证实了IL-23在人类CD4+T细胞中产生这些细胞的重要性。此外，我们还利用Solexa测序技术对人类Th1和Th17细胞亚群中的DNA酶超敏感部位进行了全基因组分析。我们的结果表明，使用这项技术，我们可以识别转录因子结合部位，并在单个T细胞亚群中区分表观遗传标记。在这项提案中，我们将检验我们的主要假设，即TH17/g细胞是中枢神经系统特异性自身免疫中的致病细胞，由IL-23通过AhR依赖的机制驱动，并在MS患者中存在选择性基因改变。总而言之，这项研究的完成不仅将描绘Th17/g细胞在自身免疫中的功能，还将确定这些细胞在小鼠和人类中产生和调节的机制。

DESCRIPTION (provided by applicant): Multiple sclerosis (MS) and its mouse model (experimental autoimmune encephalomyelitis; EAE) are autoimmune diseases of the central nervous system initiated and propagated by auto-reactive CD4+ T cells. Two subsets of CD4+ T cells, Th1 and Th17 cells have been implicated in the pathogenicity of autoimmune diseases and in particular MS. However, the relative contribution of myelin specific Th1 and Th17 cells in the development of central nervous system (CNS) autoimmunity remains controversial since neither IL-17F, IL- 17A, nor IFN-g deficient mice are fully protected from the development of CNS autoimmunity. In contrast, IL- 23p19- and IL-23 receptor (IL-23R) deficient mice are highly resistant to the development of EAE. Furthermore, in inflamed tissues of patients with autoimmune diseases, Th cells co-expressing IFN-g and IL-17 have been identified in significant number. Their increase frequency in target tissues during autoimmunity suggests an important role of these cells in the disease process. However, the genesis, stability and function of these cells in autoimmunity remain enigmatic. We have determined that most CNS-infiltrating T cells during the course of EAE express the IL-23R irrespective of their cytokine production (IL-17 and/or IFN-g) because they originate from Th17 cells. We further show that IL-23 plays a critical role in Th17 plasticity as it promotes the emergence of IL-17+ IFN-g+ T cells (Th17/g) from Th17 cells. Although Th17/g cells expressed T-bet, IFN-g production in these cells was not controlled by T-bet or other IFN-g-promoting transcription factors. In contrast, we identified AhR as a key transcription factor driving the production of IFN-g by Th17 cells in response to IL-23. We have also confirmed the importance of IL-23 for the generation of these cells in human CD4+ T cells. In addition, we have initiated a genome-wide analysis of DNase hypersensitivity sites in human Th1 and Th17 cells subsets using Solexa sequencing. Our results show that we can identify transcription factors binding sites and distinguish epigenetic marks in individual T cell subsets using this technique. In this proposal, we will test our overarching hypothesis that TH17/g cells are pathogenic cells in CNS-specific autoimmunity, are driven by IL-23 through an AhR-dependent mechanism and present with selective genetic alterations in MS patients. Together the completion of this study will not only delineate the function of Th17/g cells in autoimmunity but also determine the mechanisms by which these cells are generated and can be regulated in mice and humans.