Elimination of Toxoplasma gondii cysts by T cells

描述（由申请人提供）：刚地弓形虫是一种重要的慢性感染，能够在免疫功能低下的宿主中引起危及生命的疾病。感染持续存在的基础是组织囊肿，它优先在大脑中形成，在宿主的生命中基本上保持静止，但可以重新激活并引起疾病。为了了解弓形虫的耐药机制，有必要分析对组织囊肿的免疫反应。但是，关于这方面的资料相当有限。为了填补这一空白，我们最近开发了一种新的小鼠模型来检查免疫细胞对弓形虫囊肿的活性，发现免疫T细胞很可能有能力从感染小鼠的大脑中去除囊肿。这些结果表明，有可能开发出一种疫苗来消除慢性感染患者的组织囊肿。因此，在本提案中，具体目标旨在解决三个主要问题，以获得开始理解T细胞介导的弓形虫囊肿消除机制所必需的基本信息。第一个具体目标是确定是否需要CD4+ T细胞，CD8+ T细胞，或两者都需要从大脑中消除弓形虫囊肿。我们将利用体内生物发光成像的新技术：具体来说，我们将确定从T细胞缺陷小鼠的大脑中去除表达荧光素酶的弓形虫包囊需要过继转移的T细胞的哪个亚群。在第二个特定目标中，我们将定义介导从大脑中消除弓形虫囊肿的T细胞机制。我们将把缺乏IFN-3、穿孔素或Fas配体的突变小鼠的免疫T细胞转移到感染了表达荧光素酶的寄生虫的T细胞缺陷小鼠中，并通过体内生物发光成像监测受体囊肿负荷的变化。第三个具体目标是确定弓形虫的基因型是否影响T细胞介导的脑囊肿清除。弓形虫有三种主要的基因型（I、II和III），每一种都能感染人类。因此，确定T细胞是否以基因型特异性的方式识别和消除囊肿是很重要的，特别是从临床方面来看。为了解决这一点，我们将研究从感染II型寄生虫的小鼠身上获得的免疫T细胞的转移是否会消除大脑中的III型囊肿。这三个特定目标的研究将为免疫系统靶向弓形虫囊肿提供突破性信息，并大大提高我们对寄生虫耐药性的理解。这一信息也将对开发一种新型疫苗至关重要，以消除已经感染的患者的囊肿，并防止在新获得性感染后建立弓形虫慢性感染。

DESCRIPTION (provided by applicant): Toxoplasma gondii establishes an important chronic infection capable of causing life-threatening disease in immunocompromised hosts. The basis of persistence of the infection is the tissue cyst, which is preferentially formed in the brain and remains largely quiescent for the life of the host, but can reactivate and cause disease. To understand the mechanisms of resistance against T. gondii, it is essential to analyze the immune responses to the tissue cyst. However, the information on in this regard is quite limited. To fill this gap, we recently developed a new murine model to examine the activity of immune cells against T. gondii cysts and found that immune T cells most likely have the ability to remove the cysts from the brain of infected mice. These results suggest that it might be possible to develop a vaccine to eliminate the tissue cysts from chronically infected patients. Thus, in this proposal, the specific aims are designed to address three main questions to obtain fundamental information essential for beginning to understand the mechanisms of the T cell-mediated elimination of T. gondii cysts. The first specific aim is to determine whether CD4+ T cells, CD8+ T cells, or both subsets, are required for the elimination of T. gondii cysts from the brain. We will utilize the novel technique of in vivo bioluminescence imaging: specifically, we will determine which subset(s) of adoptively transferred T cells are required for removal of luciferase-expressing T. gondii cysts from the brains of T cell-deficient mice. In the second specific aim, we will define the T cell mechanisms that mediate the elimination of T. gondii cysts from the brain. We will transfer immune T cells from mutant mice deficient in IFN-3, perforin or Fas- ligand into T cell-deficient mice infected with luciferase-expressing parasites and monitor changes in cyst burden in the recipients by in vivo bioluminescence imaging. The third specific aim is to determine if the genotype of T. gondii affects the T cell-mediated removal of cysts from the brain. T. gondii has three predominant genotypes (I, II and III), each of which can infect humans. Thus, it is important, especially from clinical aspects, to determine if T cells recognize and eliminate cysts in a genotype-specific manner. To address this point, we will examine whether a transfer of immune T cells obtained from mice infected with a type II parasite eliminates type III cysts from the brain. The studies in these three specific aims will provide groundbreaking information on the targeting of T. gondii cysts by the immune system and dramatically improve our understanding of resistance to the parasite. This information will also be crucial for developing a novel vaccine to eliminate cysts from patients who have already been infected and to prevent establishment of chronic infection with T. gondii after a newly acquired infection.