Mycobacterial Dissemination and Persistence

描述(申请人提供)：全球结核病的高发病率是由于许多因素，包括艾滋病患者合并感染的高频率、耐药性的持续出现、治疗方案的不完全消毒活性以及结核分枝杆菌(Mtb)无限期存活的能力。肺外结核病发病率的增加是一个严重的公共卫生问题，因为它的死亡率较高，而且需要延长治疗时间。艾滋病毒和结核病的高混合感染率可能是肺外结核病发病率增加的一个原因，因为扩散发生在50%的艾滋病患者中，而在艾滋病毒阴性的人中只有5%-20%。粟粒结核病是一种严重的结核病，发生在大约8%的肺外病例中，死亡率要高得多。这些观察表明，传播是结核病严重程度的一个关键因素。由于导致再次激活的病变是继发性病变，播散在潜伏感染的建立中也发挥着重要作用，潜伏感染影响着世界近三分之一的人口。尽管传播对疾病的严重性和潜伏期的建立很重要，但其中涉及的分子机制却知之甚少。为了更好地了解结核病是如何传播的，以及这些机制是否会导致更严重的疾病和/或导致潜伏期，我们计划识别和表征这两个过程中涉及的分枝杆菌因素。关于结核病的传播方式，有四种不同的假说：1)通过迁移中的巨噬细胞/树突状细胞内的上皮细胞，2)直接侵入上皮细胞，3)上皮细胞病变和炎症反应导致通透性，4)肉芽肿侵入血管，允许细菌/感染细胞释放。目前，只有一种Mtb基因hbhA已被确定影响传播。我们自己和其他人的工作表明，分枝杆菌有许多影响巨噬细胞和上皮细胞感染效率的基因。研究还表明，结核分枝杆菌和其他分枝杆菌在上皮细胞和吞噬细胞内的生长增强了它们感染巨噬细胞的能力。宿主细胞感染的许多调节和构成机制的存在表明，参与组织侵袭和传播的分枝杆菌基因谱仍有待确定。我们的具体目标是：1)确定Mtb基因与血行播散有关，2)详细比较小鼠和豚鼠的播散情况，3)剖析Mel2基因影响播散和持久性的分子机制。我们将利用我们的跨学科团队在分枝杆菌分子遗传学、组织培养模型和动物模型方面的经验，深入了解传播和持久性的分子基础，这是结核病发病机制的关键阶段。公共卫生相关性：结核病仍然是全世界人类发病和死亡的最重要原因之一，感染了世界近三分之一的人口，每年造成200多万人死亡。潜伏感染是大多数感染者的罪魁祸首，由于细菌传播到其他组织而引起的肺外感染的死亡率更高。目前的建议侧重于了解传播是如何发生的，以及它与潜伏期的关系，以便我们能够更好地治疗、预防和诊断结核病。

DESCRIPTION (provided by applicant): The high incidence of tuberculosis worldwide is due to a number of factors, including the high frequency of co-infection in AIDS patients, continued emergence of drug resistance, incomplete sterilizing activity of therapeutic regimen and the ability of M. tuberculosis (Mtb) to persist in the host indefinitely. The increasing incidence of extrapulmonary tuberculosis is a grave public health concern because of its higher mortality rates and the need for extended therapy. High HIV-tuberculosis co-infection rates are a likely cause of the increasing incidence of extrapulmonary tuberculosis, since dissemination occurs in >50% of AIDS patients, but only 5-20% in HIV-negative individuals. Miliary tuberculosis, a severe form of tuberculosis occurring in approximately 8% of the extrapulmonary cases, has a much higher rate of mortality. These observations suggest that dissemination is a key factor in the severity of tuberculosis. Since lesions that lead to reactivation are secondary lesions, dissemination also plays an important role in establishment of latent infections, which affect nearly one-third of the world's population. Despite the importance of dissemination in the severity of disease and establishment of latency, the molecular mechanisms involved are poorly understood. In order to better understand how tuberculosis disseminates and whether these mechanisms result in greater disease severity and/or contribute to latency, we plan to identify and characterize the mycobacterial factors involved in both processes. There are four alternative hypotheses regarding how dissemination might occur in tuberculosis: 1) transit through the epithelium within migrating macrophages/dendritic cells, 2) direct invasion of the epithelium, 3) cytopathic and inflammatory response in epithelium leading to permeability, and 4) encroachment of granulomas into vessels allowing release of bacteria/infected cells. Currently, only a single Mtb gene, hbhA, has been identified that affects dissemination. Our own work and that of others indicate mycobacteria have numerous genes that affect the efficiency of macrophage and epithelial cell infection. It has also been shown that growth of Mtb and other mycobacterial species within epithelial cells and phagocytic cells enhances their ability to infect macrophages. The presence of numerous regulated and constitutive mechanisms of host cell infection suggest there is a spectrum of mycobacterial genes involved in tissue invasion and dissemination that remain to be identified. Our specific aims are to: 1) identify the Mtb genes involved in hematogenous spread from the lung, 2) detailed comparison of dissemination in mice and guinea pigs, and 3) dissect the molecular mechanisms by which the mel2 locus affects dissemination and persistence. We will take advantage of our interdisciplinary team's experience in mycobacterial molecular genetics, tissue culture models and animal models to provide insight into the molecular basis of dissemination and persistence, which are critical stages of tuberculosis pathogenesis. PUBLIC HEALTH RELEVANCE: Tuberculosis remains one of the most important causes of morbidity and mortality in humans worldwide, infecting nearly one-third of the world's population and causing more than two million deaths each year. Latent infections are responsible for the majority of those individuals infected and mortality is higher in extrapulmonary infections that arise from dissemination of the bacteria to other tissues. The current proposal is focused on understanding how dissemination occurs and its relationship to latency so that we can better treat, prevent and diagnose tuberculosis.