Regulation of memory T cell responses during Ehrlichiosis

描述（由申请人提供）：人类嗜单核细胞性埃利希体病（HME）是由革兰氏阴性专性细胞内细菌沙菲埃利希体引起的最常见的新发蜱传传染病。拟议的研究将利用两种特定的埃利希菌菌株；引起持续性感染的murichia和引起致命或亚致命感染的卵形伊氏蜱（IOE），取决于接种剂量和途径。这些模型忠实地概括了轻度和重度HME。我们的研究表明，持续感染鼠e.m is的小鼠，而不是缺乏持续感染的小鼠或感染亚致死性IOE感染但未能建立持续感染的小鼠，确实可以抵抗正常致死剂量IOE的异源再攻击。异源保护主要由CD4+ 1型记忆反应和抗原特异性IgG抗体反应介导，而致命性的原发性和继发性埃立克体病是由于埃立克体特异性CD8+ T细胞介导的广泛组织损伤。我们的初步数据显示，持续的鼠大肠杆菌感染与T调节细胞的大量扩增、脾脏中tgf - β的产生增加以及感染后免疫介导的病理缺失有关。这些数据表明，我们对控制保护性T细胞记忆的诱导和维持以及防止继发性攻击时免疫病理发展的调节机制缺乏基本的了解，而这是开发有效的HME疫苗的先决条件。我们将在以下两个具体目标中解决这一知识差距。在特定目标1中，我们将确定C57BL/6小鼠在存在或不存在持续性埃利希病毒感染时维持的记忆T细胞的大小、表型和功能。特异性目的2将确定T调节细胞和tgf - β在内皮细胞感染持续、器官损伤预防和T细胞保护性记忆反应维持中的作用。实验采用先进的技术，如多参数流式细胞术。我们的研究具有重要意义，因为它解决了在设计有效的疫苗接种策略时平衡保护性免疫和免疫病理学的强烈需求。由此产生的知识不仅有利于针对埃利希氏体的疫苗开发工作，也有利于针对由细胞介导的免疫控制的其他细胞内病原体的疫苗开发工作，这将对健康产生重大影响。

DESCRIPTION (provided by applicant): Human monocytotropic ehrlichiosis (HME) is the most prevalent emerging tick-borne infectious disease caused by Ehrlichia chaffeensis, Gram negative obligate intracellular bacteria. The proposed studies will utilize two specific Ehrlichia strains; Ehrlichia muris, which causes persistent infection, and Ixodes ovatus Ehrlichia (IOE), which causes either lethal or sub-lethal infection, depending on the dose and route of inoculation. These models faithfully recapitulate mild and severe HME. Our studies have revealed that mice persistently infected with E. muris, but not mice that lack persistent infection or mice infected with the sub-lethal IOE infection that fails to establish persistent infection, are indeed protected against heterologous re-challenge with ordinarily lethal dose of IOE. Heterologous protection is mediated primarily by CD4+ type-1 memory responses and antigen specific IgG antibody response, while fatal primary and secondary ehrlichiosis is due to an extensive tissue injury mediated by Ehrlichia specific CD8+ T cells. Our preliminary data reveal that persistent E. muris infection is associated with substantial expansion of T regulatory cells, increased TGF-beta production in the spleens, and absence of immune mediated pathology following infection with IOE. These data indicate that we lack the fundamental understanding of the regulatory mechanisms that control the induction and maintenance of protective T cell memory and prevent the development of immunopathology upon secondary challenge, which is a prerequisite to developing an effective vaccine against HME. We will address this specific gap in our knowledge in the following two specific aims. In specific aim 1, we will determine the magnitude, phenotype, and function of memory T cells maintained in the presence or absence of persistent ehrlichial infection in C57BL/6 mice. Specific aim 2 will determine the role of T regulatory cells and TGF-beta in the persistence of ehrlichial infections, prevention of organ injury, and maintenance of protective memory T cell responses. The experiments utilize state-of-the art techniques such as multiparamter flow cytometry. Our study is significant as it address the strong need for balancing protective immunity and immunopathology in designing effective vaccination strategies. Knowledge generated therein will benefit vaccine development efforts not only against Ehrlichia but also, against other intracellular pathogens that are controlled by cell mediated immunity, which will significantly have major health impact. PUBLIC HEALTH RELEVANCE: Human monocytic ehrlichiosis is a major public health problem in many parts of the United States, due in part to the lack of a vaccine and inadequate therapy. The development of a vaccine for HME is lacking due to limited understanding of how to stimulate the memory T cells required for vaccine induced immunity. This proposal will determine how memory T cells are generated, maintained and regulated using a unique experimental animal model of the disease. The results from these experiments will provide a solid foundation of knowledge for the timely development of an effective and safe vaccine against ehrlichiosis.