Masters of immunology- how Toxoplasma gondii directly manipulates T cell activation

项目摘要 免疫记忆是我们的免疫系统以更大的强度和速度做出反应的能力 再次遇到相同的病原体时（即继发感染）。免疫记忆是 疫苗接种仍然是预防传染病最成功的方法。然而，一个全面的保护 迄今为止还没有实现预防任何人类寄生虫病的疫苗。为什么绝育免疫 寄生病原体那么难实现？我们以前对顶复门菌继发感染的研究 弓形虫的研究表明，寄生虫毒力因子是逃避适应性免疫的关键 应答而抗原变异是原生动物病原体如非洲 锥虫、疟原虫和贾第虫逃避B细胞介导的抗体应答， 操纵T细胞反应的毒力因子。考虑到CD8 T细胞介导的免疫对免疫缺陷的核心作用， 广泛种类的原生动物病原体，包括T.弓形虫，该提案旨在发现寄生虫毒力 操纵CD8 T细胞反应的因素。在这里，我们报告说，T。弓形虫分泌的效应子，ROP 5和a 第二个决定子我们称之为“ROCTR”（CD8 T细胞应答调节因子），其作用是抑制T。弓形虫特异性 CD8 T细胞对寄生虫感染细胞的反应。ROP 5是假激酶的多基因可变家族， 注射到它所侵入的宿主细胞中。入侵后，T。弓形虫形成一个寄生虫空泡（PV）， 内复制。ROP 5定位于PV膜（PVM）的胞质侧，保护其免受破坏 通过宿主的IFN γ诱导的免疫相关GTP酶（IRGs）。进入MHC1抗原的蛋白质 呈递途径的蛋白质主要来源于被宿主蛋白酶体降解的胞质蛋白。 顶复门寄生虫将自己隔离在非融合PV中，大多缺乏宿主蛋白。如何 免疫系统是否能够接触到在常规内吞作用中不存在的空泡抗原， 细胞的细胞？我们的中心假设是T.弓形虫ROP 5和IRG与MHC 1相交 抗原呈递途径，T.弓形虫ROCTR可能调节这一过程。然而，T. 调节CD8 T细胞活化的弓形虫ROCTR和宿主IRG是未知的。这项建议旨在 找出这些因素。通过分析来自具有单一T细胞受体的T57小鼠的CD8 T细胞， 对T.弓形虫TGD05796 - 103/Kb抗原复合物中，T57 T细胞分泌IFN γ， 响应T。以菌株依赖性方式感染巨噬细胞。使用最新的方法， 基因组工程和寄生虫遗传学，我们将阐明T.弓形虫和 确定宿主对空泡化病原体的MHC1抗原呈递的需求。通过仔细 解剖，T的“盔甲上的裂缝”。弓形虫可能会被发现，并深入了解疫苗设计， 顶复门病原体

PROJECT SUMMARY Immunological memory is the ability of our immune system to respond with greater strength and quickness upon re-encounter with the same pathogen (i.e. secondary infection). Immunological memory is the basis for vaccination which remains the most successful method for preventing infectious disease. Yet, a fully protective vaccine to prevent any human parasitic disease has not been realized to date. Why is sterilizing immunity to parasitic pathogens so difficulty to achieve? Our previous work on secondary infections with the apicomplexan parasite, Toxoplasma gondii, suggests that parasitic virulence factors are the key to evading adaptive immune responses. Whereas antigenic variation is a major mechanism by which protozoan pathogens such as African Trypanosomes, Plasmodium and Giardia evade B cell-mediated antibody responses, little is known regarding virulence factors that manipulate T cell responses. Given the central role of CD8 T cell-mediated immunity to a wide variety of protozoan pathogens, including T. gondii, this proposal aims to discover parasitic virulence factors that manipulate CD8 T cell responses. Here we report that T. gondii secreted effectors, ROP5 and a second determinant we name ‘ROCTR’ (Regulator Of CD8 T Cell Responses), work to inhibit T. gondii-specific CD8 T cell responses to parasite-infected cells. ROP5 is a multigene variable family of pseudokinases that are injected into the host cell it invades. Following invasion, T. gondii forms a parasitophorous vacuole (PV) that it replicates within. ROP5 localizes to the cytosolic side of the PV membrane (PVM) protecting it from destruction by the host’s IFNγ-induced Immunity Related GTPases (IRGs). Proteins that enter the MHC1 antigen presentation pathway are mainly derived from cytosolic proteins that are degraded by the host’s proteasome. Apicomplexan parasites sequester themselves in a non-fusogenic PV, mostly devoid of host proteins. How does the immune system gain access to vacuolar antigens that are not within conventional endocytic compartments of the cell? Our central hypothesis is that T. gondii ROP5 and an IRG intersect the MHC1 antigen presentation pathway, and that T. gondii ROCTR may regulate this process. However, the identities T. gondii ROCTR and the host IRGs that regulate CD8 T cell activation are unknown. This proposal aims to identify these factors. By analyzing CD8 T cells from T57 mice, which possess a single T cell receptor specificity for the T. gondii TGD05796-103 / Kb antigen complex, T57 T cells were found to secrete IFNγ in response to T. gondii-infected macrophages in a strain dependent manner. Using the latest approaches in genome engineering and parasite genetics, we will elucidate mechanisms of immune evasion by T. gondii and determine host requirements for MHC1 antigen presentation of vacuolated pathogens. Through careful dissection, a ‘chink in the armor’ of T. gondii may be revealed, and give insight into vaccine design for apicomplexan pathogens.