Elimination of Toxoplasma gondii cysts by T cells

描述(申请人提供)：弓形虫建立一种重要的慢性感染，能够在免疫受损的宿主中引起危及生命的疾病。持续感染的基础是组织囊肿，它优先在大脑中形成，在宿主的一生中基本上保持静止，但可以重新激活并导致疾病。为了了解弓形虫的耐药机制，分析其对组织包囊的免疫应答是必不可少的。然而，关于这方面的信息相当有限。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测免疫细胞对弓形虫包囊的活性，并发现免疫T细胞很可能具有从感染的小鼠的大脑中移除包囊的能力。这些结果表明，开发一种疫苗来消除慢性感染患者的组织包囊是可能的。因此，在这项提案中，具体目标旨在解决三个主要问题，以获得开始了解T细胞介导的消除弓形虫包囊的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，或两者兼而有之，才能从大脑中消除弓形虫包囊。我们将利用体内生物发光成像的新技术：具体地说，我们将确定从T细胞缺陷小鼠的大脑中移除表达荧光素酶的弓形虫包囊需要过继转移的T细胞亚群(S)。在第二个具体目标中，我们将定义T细胞机制，它介导了弓形虫包囊从脑中的清除。我们将把缺乏干扰素-3、穿孔素或Fas-配体的突变小鼠的免疫T细胞转移到表达荧光素酶的寄生虫感染的T细胞缺陷小鼠中，并通过体内生物发光成像监测受体体内包囊负荷的变化。第三个具体目标是确定弓形虫的基因是否会影响T细胞介导的脑囊肿清除。弓形虫有三种主要的基因类型(I、II和III)，每一种都可以感染人类。因此，重要的是，特别是从临床方面，确定T细胞是否以一种特定的基因型别的方式识别和消除囊肿。为了解决这一问题，我们将研究从感染II型寄生虫的小鼠身上获得的免疫T细胞转移是否可以消除脑内III型包囊。这三个特定目标的研究将提供免疫系统靶向弓形虫包囊的突破性信息，并极大地提高我们对这种寄生虫耐药性的理解。这些信息对于开发一种新的疫苗也将是至关重要的，该疫苗可以消除已经感染的患者的包囊，并防止在新感染后出现弓形虫的慢性感染。

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.