IFN-gamma production by microglia for prevention of toxoplasmic encephalitis

描述（由申请方提供）：免疫功能低下个体脑中慢性弓形虫感染的再激活导致危及生命的弓形虫脑炎（TE）的发展。为了改善TE的预防和管理，重要的是要了解疾病的免疫发病机制。我们开发的TE小鼠模型提供了一个极好的机会来批判性地分析大脑中宿主防御机制。据文献记载，募集到脑中的T细胞是用于预防TE的IFN-3的重要来源。然而，在大量T细胞进入大脑之前，宿主防御在感染重新激活的早期阶段如何发挥作用尚不清楚。这种早期防御系统可能对限制速殖子生长和启动T细胞免疫以防止TE至关重要。我们最近发现，小胶质细胞，这是居民在脑实质中的巨噬细胞，产生IFN-3的早期阶段的再激活。我们的研究还表明，除了T细胞外，脑特异性细胞产生IFN-3也是预防TE所必需的。因此，小胶质细胞产生IFN-3似乎是预防该疾病所必需的一种新的早期防御机制。本提案的具体目的是确定小胶质细胞产生的IFN-3在抑制速殖子生长、诱导T细胞免疫和预防TE中的作用。在第一个目标中，我们将研究小胶质细胞产生的IFN-3对感染再激活后大脑中速殖子增殖的抑制作用，使用仅由小胶质细胞产生IFN-3的小鼠。第二个目的是确定小胶质细胞产生的IFN-3是否诱导将T细胞募集到大脑中的介质的表达。我们将研究小胶质细胞产生IFN-3是否诱导脑细胞中趋化因子和脑血管内皮细胞上粘附分子的表达。然后，我们将使用体内T细胞迁移试验来确定小胶质细胞产生的IFN-3是否有助于免疫T细胞浸润到大脑中。第三个目的是确定小胶质细胞产生的IFN-3是否诱导MHC分子的表达以激活脑中的T细胞。在第四个目标中，我们将确定小胶质细胞和T细胞产生IFN-3以预防TE的需要。为此，我们将从感染的野生型或IFN-3缺陷型小鼠中纯化免疫T细胞，并将这些T细胞转移到仅通过小胶质细胞表达IFN-3或缺乏这种细胞因子表达的感染小鼠中。将跟踪宿主小鼠的TE发展。我们还将研究IFN-3依赖性介导的T细胞募集在预防TE的具体目标2中确定的作用。这四个具体目标的研究将提供新的和关键的信息，使我们能够了解小胶质细胞如何产生IFN-3，使大脑中的宿主防御系统能够预防TE。公共卫生相关性免疫功能低下个体脑内慢性弓形虫感染的再激活可导致危及生命的弓形虫脑炎（TE）的发展。拟议的研究是分析脑细胞（小胶质细胞）如何抑制寄生虫生长并诱导免疫反应以预防TE。这些信息将有助于更好地了解TE的免疫发病机制，并改善疾病的预防和管理。

DESCRIPTION (provided by applicant): Reactivation of chronic Toxoplasma gondii infection in the brains of immunocompromised individuals results in the development of life-threatening toxoplasmic encephalitis (TE). To improve prevention and management of TE, it is important to understand the immunopathogenesis of the disease. The murine models of TE that we developed provide an excellent opportunity to critically analyze the mechanisms of host defense in the brain. It is well documented that T cells recruited into the brain are an essential source of IFN-3 for prevention of TE. However, it is not known how the host defense functions during the early stage of reactivation of infection before large numbers of T cells enter the brain. This early defense system could be crucial for limiting tachyzoite growth and initiating T cell immunity to prevent TE. We recently found that microglia, which are resident macrophages in the brain parenchyma, produce IFN-3 during the early stage of reactivation. Our studies also suggest that production of IFN-3 by brain-specific cells, in addition to T cells, is required for prevention of TE. Therefore, IFN-3 production by microglia appears to be a novel early defense mechanism essential for prevention of the disease. The specific aims in this proposal are designed to define the role of IFN-3 produced by microglia in inhibition of tachyzoites growth, induction of T cell immunity, and prevention of TE. In the first aim, we will examine the inhibitory effects of IFN-3 produced by microglia on tachyzoite proliferation in the brain after reactivation of infection using mice that have IFN-3 production only by microglia. The second aim is to determine if IFN-3 production by microglia induces expression of mediators that recruit T cells into the brain. We will examine whether IFN-3 production by microglia induces expression of chemokines in brain cells and adhesion molecules on cerebrovascular endothelial cells. We will then use in vivo T cell migration assays to determine whether IFN-3 production by microglia facilitates infiltration of immune T cells into the brain. The third aim is to determine if IFN-3 production by microglia induces expression of MHC molecules for activation of T cells in the brain. In the fourth aim, we will determine the requirement of IFN-3 production by microglia and T cells for prevention of TE. For this purpose, we will purify immune T cells from infected wild-type or IFN-3-deficient mice and transfer these T cells into infected mice that express IFN-3 only by microglia or lack expression of this cytokine. Host mice will be followed for development of TE. We will also examine the role of IFN-3-dependent mediators of T cell recruitment determined in Specific Aim 2 for prevention of TE. The studies in these four specific aims will provide novel and crucial information that allows us to understand how IFN-3-production by microglia enables the host defense system in the brain to prevent TE. PUBLIC HEALTH RELEVANCE Reactivation of chronic Toxoplasma gondii infection in the brains of immunocompromised individuals results in the development of life-threatening toxoplasmic encephalitis (TE). The proposed studies are to analyze how brain cells (microglia) inhibit parasite growth and induce the immune responses to prevent TE. This information will contribute to better understanding of the immunopathogenesis of TE and to improved prevention and management of the disease.