Innate Regulation and CD4+Th1/17 Immunity in TMEV-Induced Demyelination

描述（由申请人提供）：Theiler's小鼠脑脊髓炎病毒（TMEV）诱导的脱髓鞘病（TMEV- idd）被广泛认为是病毒诱导的自身免疫介导的脱髓鞘病最相关的动物模型。多发性硬化症被认为与自身免疫病理有关，但流行病学证据强烈提示病毒触发。TMEV是小鼠的天然病原体，易感SJL小鼠脑内接种TMEV BeAn株可导致慢性进行性炎症免疫介导的脱髓鞘疾病，该疾病与终身持续性中枢神经系统病毒感染有关，以痉挛性后肢瘫痪为特征。相比之下，耐药C57BL/6小鼠产生有效的CTL反应并迅速清除感染。与MS一样，TMEV-IDD的特征是进行性脱髓鞘，并伴有以CD4+ T细胞和活化的apc（小胶质细胞/巨噬细胞/DCs）为主的单核细胞浸润。我们之前的研究表明，脱髓鞘是由病毒特异性CD4+ T细胞靶向持续感染的中枢神经系统APCs所呈现的病毒表位引发的。慢性脱髓鞘是通过对多种内源性脑源性髓鞘表位的自身免疫反应的诱导介导的，这些反应是通过表位扩散产生的。本申请建议继续我们在过去21年中由NIH PPG资助的生产性研究。基于大量新的初步数据，我们将研究先天免疫调节和先天免疫刺激机制在调节TMEV-IDD易感性/抗性方面的作用，包括免疫介导的病毒对急性感染的清除水平和慢性脱髓鞘过程中自身免疫过程的调节。利用耗竭、补充和遗传方法，Aim 1将验证CD4+CD25+Foxp3+ Tregs的激活在调节TMEV-IDD易感性中起主要作用的假设，通过抑制急性感染期间病毒特异性CD4、CD8和抗体反应的发展，导致中枢神经系统病毒持久性的建立，从而最终发展为慢性自身免疫。Aim 2将验证髓鞘表位特异性自身反应性Th1 （IFN-3）和Th17 （IL-17）细胞的促炎作用在TMEV-IDD慢性自身免疫性阶段介导脱髓鞘免疫病理的关键。在慢性TMEV-IDD中，外周来源的CNS驻留dc在驱动表位扩散到髓磷脂特异性CD4+ Th1/17细胞的激活中发挥关键作用。先天免疫反应（细胞因子、趋化因子和抗原呈递分子的表达）；检测tmev感染小鼠cns来源的dc、MUs和小胶质细胞激活T细胞增殖和幼稚CD4、记忆CD4+ （Th1、Th2和Th17）和CD8+ T细胞分化的功能能力。这些研究将为病毒诱导脱髓鞘的易感性/耐药机制提供重要信息，并适用于未来设计MS和其他中枢神经系统炎症性疾病的治疗策略。

DESCRIPTION (provided by applicant): Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease (TMEV-IDD) is widely considered the most relevant animal model of virus-induced autoimmune-mediated demyelinating disease. MS is believed to involve an autoimmune pathology, but epidemiological evidence strongly suggests a viral trigger. TMEV are natural mouse pathogens and intracerebral inoculation of susceptible SJL mice with the BeAn strain of TMEV results in a chronic-progressive, inflammatory immune-mediated demyelinating disorder which is related to life-long persistent CNS virus infection and characterized by spastic hind limb paralysis. In contrast, resistant C57BL/6 mice make a potent CTL response and rapidly clear the infection. Like MS, TMEV-IDD is characterized by progressive demyelination with accompanying mononuclear cell infiltrates dominated by CD4+ T cells and activated APCs (microglia/macrophages/DCs). Our previous studies have shown that demyelination is initiated by virus-specific CD4+ T cells targeting viral epitopes presented by persistently infected CNS- resident APCs. Chronic demyelination is mediated by induction of autoimmune responses to a variety of endogenous encephalitogenic myelin epitopes which arise via epitope spreading. This application proposes continue our productive studies funded by an NIH PPG for the past 21 years. Based on extensive new preliminary data, we will examine the role of innate immune regulatory and innate immune stimulatory mechanisms involved in regulating susceptibility/resistance to TMEV-IDD at both the level of immune- mediated virus clearance to acute infection and regulation of autoimmune processes during chronic demyelination. Employing depletion, supplementation and genetic approaches, Aim 1 will test the hypothesis that activation of CD4+CD25+Foxp3+ Tregs plays a major role in regulating susceptibility to TMEV-IDD by inhibiting development of virus-specific CD4, CD8, and antibody responses during acute infection leading to establishment of CNS virus persistence and hence eventual development of chronic autoimmunity. Aim 2 will test the hypothesis that the pro-inflammatory effects of both myelin epitope-specific autoreactive Th1 (IFN-3) and Th17 (IL-17) cells are critical for mediating demyelinating immunopathology during the chronic autoimmune phase of TMEV-IDD. Aim 3, will test the hypothesis that peripherally-derived, CNS-resident DCs play a critical role in driving the activation of epitope spreading to myelin-specific CD4+ Th1/17 cells responsible for CNS pathology in chronic TMEV-IDD. Innate immune responses (expression of cytokines; chemokines; and antigen presentation molecules); and functional ability of CNS-derived DCs, MUs and microglia from TMEV-infected mice to activate T cell proliferation and differentiation of naove CD4 and memory CD4+ (Th1, Th2 and Th17) and CD8+ T cells by will be determined. These studies will provide important information on the mechanisms underlying susceptibility/resistance in virus-induced demyelination and are applicable for the future design of treatment strategies for MS and other CNS inflammatory diseases. PUBLIC HEALTH RELEVANCE: Multiple sclerosis (MS) is an autoimmune paralytic disease caused by immune cell-mediated destruction of myelin-producing oligodendrocytes in the central nervous system. Certain forms of MS are suspected to occur as a secondary consequence a virus infection in genetically susceptible individuals. We will employ a mouse model of MS induced by infection with Theiler's murine encephalomyelitis virus to study the role of regulatory T cells in determining genetic susceptibility to disease in different strains of inbred mice, and to determine the role of dendritic cells, specialized antigen presenting cells of the innate immune system, both in inducing virus immunity in the acute stages of the disease and in inducing development of autoimmune T cells making destructive cytokines (IFN-3 and IL-17) in the chronic phase of disease.