Mechanisms of HIV-associated Disruption of Intestinal Homeostasis

描述（由申请方提供）：肠道微生物植物群通常以微妙的平衡与宿主共存，肠上皮细胞提供物理屏障，防止微生物进入深层组织，下层固有层（LP）中严格调节的细胞免疫系统提供保护，防止入侵的病原体或破坏上皮屏障的细菌。肠道树突状细胞（IDCs）是一种有效的抗原呈递细胞（APC），它能在先天免疫和适应性免疫之间起桥梁作用，能够对肠道细菌进行采样，并可能在介导对细菌的耐受性以及对病原体的防御中发挥关键作用。HIV-1已被证明在感染的急性阶段在肠道相关淋巴组织（GALT）中复制，导致CCR 5 + CD 4 + T细胞，特别是产生IL-17的CD 4 + T细胞（Th 17细胞）的早期、大量和持续消耗。Th 17细胞被认为是肠道炎症的介质，但也被认为通过限制肠道细菌渗透在正常粘膜防御和体内平衡中发挥作用。在慢性HIV-1感染中已经描述了细菌产物和DNA转运到体循环中，但这一过程是否影响HIV-1在肠粘膜中的复制或发病机制尚不清楚。我们已经鉴定出在正常人肠组织中响应于嗜酸菌产生IFN-3和IL-2（Th 1）或IL-17（Th 17）的人LP效应CD 4 + T细胞的显著频率。重要的是，体外细菌特异性LP CD 4 + T细胞增殖依赖于CD 1c + LP DCs的存在。该LP DC亚群显示在用模拟HIV-1 ssRNA的Toll样受体（TLR）7/8的配体刺激后产生炎性Th 17偏性细胞因子IL-23。此外，我们表明，除了细菌的HIV-1感染的固有层单核细胞（LPMC）培养导致LP CD 4 + T细胞的感染增加。 我们推测，HIV-1在肠粘膜中的复制通过与常驻IDC的相互作用破坏了肠道内稳态，通过使局部宿主对肠道细菌的反应偏离调节并朝向炎症。在这个建议中，我们将讨论HIV-1破坏肠道内稳态和细菌防御的正常过程的致病机制。具体而言，我们建议1）研究HIV-1在体外改变人类对肠道细菌的先天性和适应性反应的机制，2）定义肠道细菌在体外影响HIV-1在肠粘膜中复制的机制，3）评估粘膜免疫功能与肠粘膜和来自未治疗队列的血浆样品中细菌物种多样性之间的关系，HIV-1感染者。我们相信，从这些研究中获得的知识将大大有助于理解HIV-1的致病机制，并促进HIV-1的合理治疗，减少慢性炎症和恢复肠道免疫的发展。 公共卫生相关性：该项目的目标是了解HIV用于破坏肠道内稳态和细菌防御的正常过程的机制。

DESCRIPTION (provided by applicant): Intestinal microbial flora normally co-exist in a delicate balance with the host, with intestinal epithelial cells providing a physical barrier to prevent access of microbes to deeper tissues and a tightly regulated cellular immune system in the underlying lamina propria (LP) providing protection against invading pathogens or commensals that breach the epithelial barrier. Intestinal dendritic cells (IDCs), potent antigen presenting cells (APC) that bridge innate and adaptive immunity, are able to sample luminal bacteria and likely play a key role in mediating tolerance to commensals as well as defense against pathogens. HIV-1 has been shown to replicate in gut-associated lymphoid tissue (GALT) in the acute stages of infection, resulting in an early, massive, and persistent depletion of CCR5+CD4+ T cells, and in particular of IL-17-producing CD4+ T cells (Th17 cells). Th17 cells have been implicated as mediators of intestinal inflammation but are also proposed to play a role in normal mucosal defense and homeostasis by limiting commensal bacterial penetration. Translocation of bacterial products and DNA into the systemic circulation has been described in chronic HIV-1 infection, but whether this process impacts HIV-1 replication or pathogenesis in the intestinal mucosa is unknown. We have identified significant frequencies of human LP effector CD4+ T cells that produce IFN-3 and IL-2 (Th1) or IL-17 (Th17) in response to commensal bacteria in normal human intestinal tissue. Importantly, bacteria-specific LP CD4+ T cell proliferation in vitro was dependent on the presence of CD1c+ LP DCs. This subset of LP DCs was shown to produce the inflammatory, Th17-biasing cytokine IL-23 upon stimulation with ligands for Toll-like receptors (TLRs) 7/8 that simulate HIV-1 ssRNA. Furthermore, we show that addition of commensal bacteria to HIV-1-infected lamina propria mononuclear cell (LPMC) cultures resulted in increased infection of LP CD4+ T cells. We hypothesize that HIV-1 replication in the intestinal mucosa disrupts intestinal homeostasis through interactions with resident IDCs by skewing the local host response to commensal bacteria away from regulation and toward inflammation. In this proposal, we will address the pathogenic mechanisms whereby HIV-1 disrupts the normal process of intestinal homeostasis and bacterial defense. Specifically, we propose to 1) investigate the mechanisms by which HIV-1 alters human innate and adaptive responses to commensal bacteria in vitro, 2) define the mechanisms by which commensal bacteria influence HIV-1 replication in intestinal mucosa in vitro, and 3) evaluate the relationship between mucosal immune function and bacterial species diversity in intestinal mucosa and plasma samples from a cohort of untreated, HIV-1- infected subjects. We believe that the knowledge gained from these studies will contribute significantly to the understanding of HIV-1 pathogenic mechanisms and facilitate the development of rational therapies for HIV-1 that decrease chronic inflammation and restore intestinal immunity. PUBLIC HEALTH RELEVANCE: The goal of this project is to understand the mechanisms that HIV uses to disrupt the normal processes of homeostasis and bacterial defense in the gut.