Regulatory T cells dictate immunity during persistent Salmonella infection

描述(申请人提供)：伤寒是一种由宿主适应的沙门氏菌引起的持续性感染。矛盾的是，当免疫介导的损害超过感染构成的直接风险时，允许病原体持续存在也可能对宿主有利。我们的长期目标是识别在沙门氏菌感染期间激活的免疫细胞和信号，这些细胞和信号控制着根除病原体所需的免疫激活和相关的免疫介导宿主损伤风险之间的平衡，以及以牺牲病原体持久性为代价的免疫抑制。鼠伤寒沙门氏菌感染模型再现了人伤寒持续感染的重要特征。再加上大量的免疫学工具和试剂仅在小鼠身上可用，该物种的感染是目前识别控制这种微妙免疫平衡的分子和细胞信号的最佳模型。利用这个模型，我们的初步研究表明，调节性T细胞(Tregs)由以Foxp3-表达为特征的不同的CD4+T细胞谱系组成，在决定免疫激活和细菌持久性之间的平衡方面发挥着关键作用。感染后早期，Foxp3+Treg消融加速细菌清除的动力学，而增加Foxp3+Treg会导致病原菌负担的互惠增加。因此，本应用程序的总体目标是定义相对重要性，并确定在持续沙门氏菌感染过程中Tregs利用的抑制机制。目标1将扩展我们的初步发现，通过定义持续感染期间Treg抑制能力变化的综合动力学分析，显示在早期(第5天)和晚期(第37天)分离的细胞的Treg抑制能力的急剧变化。我们的具体目标是确定Treg抑制效力何时达到峰值、最低点，并恢复到基线水平，以及这些变化的绝对幅度。这些结果将为补充实验建立框架，通过量化Treg消融的相对影响来验证Treg在这些关键时间点的重要性。使用最近开发的技术重建Treg消融小鼠，供体Treg来自定义的Treg相关分子靶向缺陷的小鼠，Aim 2将进一步探索Treg抑制效力这些变化的机制基础。这些实验包括识别和分离控制宿主防御的特定Treg相关分子和维持外周免疫耐受所需的分子，并定义沙门氏菌配体和相应的模式识别受体，这些受体通过细胞内部刺激决定Treg抑制效力的这些变化。结合这些利用尖端免疫学工具的实验，不仅将填补我们目前关于Foxp3+Tregs在沙门氏菌感染期间控制宿主防御的重要性和机制的重要知识空白，而且还将为Tregs如何在其他持续感染期间调节免疫建立重要的范式。 公共卫生相关性：持续感染的发病机制由相反的免疫激活和抑制信号之间的平衡控制。利用小鼠的沙门氏菌感染作为人类伤寒的模型，这项应用试图确定调节性T细胞的重要性，并确定这些细胞在持续细菌感染期间控制这种微妙的免疫平衡的分子基础。

DESCRIPTION (provided by applicant): Typhoid fever is a persistent infection caused by host adapted Salmonella species. Paradoxically, allowing pathogen persistence may also be beneficial for the host when immune-mediated damage outweigh the immediate risk posed by the infection. Our long-term goals are to identify the immune cells and signals activated during Salmonella infection that controls this balance between immune activation required for pathogen eradication with the associated risk of immune-mediated host injury, and immune suppression at the expense of pathogen persistence. The mouse model of S. typhimurium infection reproduces important features of persistent infection characteristic of human typhoid. Together with the abundance of immunological tools and reagents available only in mice, infection in this species is currently the best-available model for identifying the molecular and cellular signals that control this delicate immunological balance. Using this model, our preliminary studies indicate regulatory T cells (Tregs) that comprise a distinct lineage of CD4+ T cells characterized by Foxp3-expression play critical roles in dictating the balance between immune activation and bacterial persistence. Early after infection, Foxp3+Treg-ablation accelerates the kinetics of bacterial eradication, while augmenting Foxp3+Tregs causes reciprocal increases in pathogen burden. Therefore the overall goals of this application are to define the relative importance and identify the suppressive mechanism utilized by Tregs throughout persistent Salmonella infection. Aim 1 will expand on our preliminary findings that demonstrate drastic changes in Treg suppressive potency for cells isolated at early (day 5) and late (day 37) time points, by defining a comprehensive kinetic analysis for changes in Treg suppressive potency during persistent infection. Our specific goals are to identify when Treg suppressive potency peaks, nadirs, and returns to baseline levels, and the absolute magnitude for these changes. These results will establish the frame-work for complementary experiments that verify the importance of Tregs at these critical time points by quantifying the relative impacts of Treg-ablation. Using recently developed techniques for reconstituting Treg- ablated mice with donor Tregs from mice with targeted defects in defined Treg-associated molecules, Aim 2 will further explore the mechanistic basis for these changes in Treg suppression potency. These include experiments that will identify and dissociate the specific Treg-associated molecules that control host defense from those required for sustaining peripheral immune tolerance, and define Salmonella ligands and the corresponding pattern recognition receptors that dictate these changes in Treg suppression potency through cell-intrinsic stimulation. Together these experiments that utilize cutting edge immunological tools will not only fill important gaps in our current knowledge on the importance and the mechanism whereby Foxp3+Tregs control host defense during Salmonella infection, but also establish important paradigms for how Tregs may regulate immunity during other persistent infections. PUBLIC HEALTH RELEVANCE: The pathogenesis of persistent infection is controlled by the balance between opposing immune activation and suppression signals. Using Salmonella infection in mice as a model of human typhoid, this application seeks to define the importance of regulatory T cells, and identify the molecular basis whereby these cells control this delicate immunological balance during persistent bacterial infection.