Mechanisms of HIV-associated Disruption of Intestinal Homeostasis

描述(申请人提供)：肠道微生物菌群通常与宿主共存，处于微妙的平衡状态，肠道上皮细胞提供物理屏障，防止微生物进入更深的组织，固有层(LP)中受到严格调控的细胞免疫系统提供保护，防止入侵的病原体或突破上皮屏障的共生体。肠道树突状细胞(IDCs)是连接天然免疫和获得性免疫的强有力的抗原提呈细胞(APC)，能够对肠道细菌进行采样，在介导对共生菌的耐受和对病原体的防御中可能发挥关键作用。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CCR5+CD4+T细胞的早期、大量和持续的耗尽，特别是产生IL-17的CD4+T细胞(Th17细胞)。Th17细胞被认为是肠道炎症的介质，但也被认为通过限制共生细菌的渗透在正常的粘膜防御和动态平衡中发挥作用。在慢性HIV-1感染中，细菌产物和DNA移位到体循环中已被描述，但这一过程是否影响HIV-1在肠道粘膜中的复制或发病机制尚不清楚。我们已经确定了人类LP效应器CD4+T细胞在正常人体肠道组织中产生干扰素-3和IL-2(Th1)或IL-17(Th17)的显著频率。重要的是，细菌特异性LP CD4+T细胞的体外增殖依赖于CD1c+LP DC的存在。当模拟HIV-1单链RNA的Toll样受体(TLRs)7/8的配体刺激时，这一亚群的LP DC可以产生炎性的、偏向Th17的细胞因子IL-23。此外，我们发现，在HIV-1感染的固有层单个核细胞(LPMC)培养中加入共生菌会导致LP CD4+T细胞的感染增加。我们假设，HIV-1在肠粘膜中的复制通过与常驻IDC的相互作用，通过扭曲当地宿主对共生细菌的反应，使其远离调节，转向炎症，从而破坏了肠道的动态平衡。在这项提案中，我们将解决HIV-1扰乱肠道内稳态和细菌防御的正常过程的致病机制。具体地说，我们建议1)研究HIV-1在体外改变人类对共生细菌的先天和适应性反应的机制，2)确定共生细菌在体外影响肠粘膜中HIV-1复制的机制，以及3)评估肠粘膜免疫功能与肠道粘膜和来自未经治疗的HIV-1感染者的血浆样本中细菌物种多样性的关系。我们相信，从这些研究中获得的知识将大大有助于了解HIV-1的致病机制，并有助于开发合理的治疗HIV-1的方法，以减少慢性炎症和恢复肠道免疫。 与公共卫生相关：这个项目的目标是了解HIV用来破坏肠道内正常的动态平衡和细菌防御过程的机制。

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.