IFN-gamma production by microglia for prevention of toxoplasmic encephalitis

描述(由申请人提供)：免疫受损个体大脑中慢性弓形虫感染的重新激活导致威胁生命的弓形体脑炎(TE)的发展。为了改善TE的预防和治疗，了解该病的免疫发病机制是重要的。我们开发的小鼠血栓栓塞症模型提供了一个很好的机会来批判性地分析大脑中宿主防御的机制。已有文献证明，T细胞被招募到大脑中是预防TE所需的干扰素-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是如何发挥作用的尚不清楚。这一早期防御系统对于限制速殖子的生长和启动T细胞免疫以预防TE至关重要。我们最近发现，小胶质细胞是驻留在脑实质中的巨噬细胞，在重新激活的早期阶段会产生干扰素-3。我们的研究还表明，除了T细胞外，大脑特定细胞还需要产生干扰素-3来预防TE。因此，小胶质细胞产生干扰素-3似乎是预防该病所必需的一种新的早期防御机制。这项建议的具体目的是确定小胶质细胞产生的干扰素-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，我们将使用仅由小胶质细胞产生干扰素-3的小鼠来检测小胶质细胞产生的干扰素-3对感染后再激活的脑内速殖子增殖的抑制作用。第二个目标是确定小胶质细胞产生的干扰素-3是否会诱导将T细胞招募到大脑中的介质的表达。我们将研究小胶质细胞产生的干扰素-3是否诱导脑细胞中趋化因子和脑血管内皮细胞上黏附分子的表达。然后，我们将使用体内T细胞迁移分析来确定小胶质细胞产生的干扰素-3是否促进免疫T细胞向大脑的渗透。第三个目标是确定小胶质细胞产生的干扰素-3是否诱导大脑中T细胞活化的MHC分子的表达。在第四个目标中，我们将确定小胶质细胞和T细胞产生干扰素-3的需要量，以预防TE。为此，我们将从感染野生型或干扰素-3缺陷的小鼠中提纯免疫T细胞，并将这些T细胞转移到仅通过小胶质细胞表达干扰素-3或缺乏该细胞因子表达的感染小鼠中。将跟踪宿主小鼠以发展成TE。我们还将研究在特定目标2中确定的依赖于干扰素-3的T细胞募集介质在预防TE中的作用。对这四个特定目标的研究将提供新的和关键的信息，使我们能够理解小胶质细胞产生的干扰素-3如何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受损个体大脑中慢性弓形虫感染的重新激活导致威胁生命的弓形体脑炎(TE)的发展。拟议的研究旨在分析脑细胞(小胶质细胞)如何抑制寄生虫的生长并诱导免疫反应来预防TE。这些信息将有助于更好地了解TE的免疫发病机制，并有助于改进对该疾病的预防和管理。

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.