An Intracellular Niche for Borrelia burgdorferi

描述（由申请人提供）：莱姆病是由螺旋体伯氏疏螺旋体引起的，是美国主要的关节传播感染，在流行地区发病率很高。如果未经治疗的伯氏疏螺旋体可以持续感染个体，即使宿主产生了强有力的适应性免疫反应，从感染患者或实验感染动物身上获得的抗体可以有效地杀死体外培养的伯氏疏螺旋体。此外，观察到一个强大的细胞介导的促炎反应，诱导IL-6， IL-12和IFN-?？抑制IL-10此外，螺旋体可以抵抗补体杀伤，这表明先天免疫反应的重要组成部分不足以消除伯氏疏螺旋体感染。观察到伯氏疏螺旋体在如此恶劣的环境中持续存在，表明螺旋体擅长通过尚未完全阐明的机制逃避宿主免疫反应。一种可能是伯氏疏螺旋体侵入宿主细胞并以低水平存活。

DESCRIPTION (provided by applicant): Lyme disease, caused by the spirochetal bacterium Borrelia burgdorferi, is the leading arthropodborne infection in the United States and causes significant morbidity in endemic areas. If untreated B. burgdorferi can persistently infect individuals even though the host mounts a potent adaptive immune response such that antibodies obtained from infected patients or experimentally infected animals effectively kills in vitro cultivated B. burgdorferi. In addition, a robust cell-mediated proinflammatory response is observed that induces IL-6, IL-12 and IFN-??and inhibits IL-10. Furthermore, the spirochete can resist complement killing demonstrating that this important component of the innate immune response is not sufficient to eliminate B. burgdorferi infection. The observation that B. burgdorferi persists in such a hostile environment indicates that the spirochete is adept at evading the host immune response via mechanisms that have not been completely elucidated. One possibility is that B. burgdorferi invades host cells and survives at low levels. Recently we have determined that B. burgdorferi invade both immortalized and, more importantly, primary cells (both fibroblasts and endothelial cells) and persist as viable cells in o-culture. In addition we have preliminary data suggesting that the ability to invade host cells involves both integrin binding and Src kinase activity. In this application we propose to further characterize the internalization of B. burgdorferi and track the fate of B. burgdorferi within thes infected cells to determine how they affect the localized host response following infection. To accomplish this we will use both in vitro correlates of invasion and intracellular survival as well as in vivo imaging of experimentally infected mice as readouts for our studies. Specifically, we propose to: (1) Characterize the invasion of Borrelia burgdorferi into primary fibroblasts. The working hypothesis here is that B. burgdorferi exploits invasion as an additional mechanism to avoid host clearance. Our preliminary studies demonstrate that B. burgdorferi invasion is not dependent on host fibronectin, but does involve ?1 integrins other than ?5?1. In this Aim we will identify the ??subunit that pairs with ?1 to promote invasion and will also evaluate how B. burgdorferi traffics within these cells; and (2) Determine if invasion is required for B. burgdorferi persistence in vivo. Our working hypothesis is that invasion contributes to persistence by providing an immunoprotected niche for B. burgdorferi. Since Src kinases are required for borrelial internalization in vitro, we will determine whether Src kinase inhibitors aler the infectivity potential of B. burgdorferi in vivo. In addition to standard cultivation and molecuar approaches, novel in vivo imaging will be employed to assess how the inhibitor affects colonization. The overall goal of these studies is to determine the extent in which an intracellula locale contributes to borrelial persistence. PUBLIC HEALTH RELEVANCE: Borrelia burgdorferi, the etiologic agent of Lyme disease, is the most common arthropod-borne infectious agent in the United States, and, as such, represents an important Public Health issue. The studies described in this application are designed to address how B. burgdorferi is able to persist effectively in infected mammals despite effective innate immune killing mechanisms and a potent adaptive immune response directed against this pathogen. The hypothesis being tested herein is that B. burgdorferi is capable of low-level intracellular survival in non-immune cells as an additional strategy to prevent borrelial host clearance.