Modulation of Human Cells by Virulent Francisella tularensis

摘要：土拉热弗朗西斯菌是土拉菌病的病原体，可通过多种途径感染人类，包括媒介传播。然而，吸入细菌和由此产生的肺炎土拉菌病是最危险的疾病形式。这是由于潜伏期短（3-5天），非特异性症状，以及未经治疗的个体的高死亡率（大于80%）。此外，F.美国和前苏联都已将土拉热病毒武器化，使其成为一种可行的生物武器。尽管对F.尽管土拉热菌在世界各地流行，但人们对这种细菌与宿主的动态相互作用，特别是在气溶胶感染后的相互作用知之甚少。 我的实验室已经证实，与鼠细胞相似，人类树突状细胞对F.土拉热，但不能产生促炎细胞因子或经历成熟。 此外，毒力F.土拉菌主动干扰人类DC对二级刺激做出反应的能力。了解F.土拉菌主动抑制DC功能是我实验室的中心指令。 我们正在以两种不同的方式处理这一指令。 首先，我们分析弗朗西斯菌脂质在介导抗炎反应中的作用。 存在于细菌表面的结构是宿主细胞遇到的第一个成分。 因此，在F.在土拉热感染中，这些结构有助于人类树突细胞的早期快速抑制。 细菌脂质就是这样一种结构。我们实验室的初步证据表明，与F。土拉热可以有效地抑制人树突细胞中的炎症反应。我们目前正在确定负责这种抑制的特定脂质以及它们干扰人类树突状细胞功能的机制。 其次，我们正在探索由F. tularensis，其通过多种途径负调节人树突状细胞。 例如，如果细胞外细菌的复制受到限制，则人树突细胞响应于其他微生物刺激而产生TNF-α的能力得以恢复。 然而，没有观察到IL-12产生的类似恢复。 我们已经证明了F.土拉热菌有效地抑制人树突细胞中IL-12的产生。我们目前正在研究IFN-β在F.土拉菌感染人树突状细胞。 除了有助于开发新的疫苗和治疗剂之外，鉴定能够负调节特定宿主途径（同时保持其他途径完整）的细菌产物可以为针对癌症和自身免疫性疾病的治疗剂提供新的靶标。 最后，宿主细胞炎性小体的活化和随后的炎性细胞因子IL-1 β和IL-18的分泌被认为是宿主防御多种病原体的中心特征。 事实上，已经表明F.土拉热菌能够激活炎性小体，导致细胞死亡和IL-1b的释放。 然而，我们的数据表明，强毒F。土拉菌逃避并干扰这一过程。 目前，我们正在研究炎性小体，IL-1b和IL-18在防御兔热病中的作用。 此外，我们的目标是确定F。土拉热破坏了这一过程。

Summary: Francisella tularensis, the causative agent for tularemia, can infect humans by a number of routes, including vector-borne transmission. However, it is inhalation of the bacterium, and the resulting pneumonic tularemia, that represents the most dangerous form of disease. This is due to the short incubation time (3-5 days), non-specific symptoms, and a high mortality rate (greater than 80%) in untreated individuals. Furthermore, F. tularensis has been weaponized by both the United States and the former Soviet Union making it a viable candidate for use as a biological weapon. Despite over 80 years of research on F. tularensis around the world, very little is understood about the dynamic interaction of this bacterium with the host, especially following aerosol infection. My laboratory has established that, similarly to murine cells, human dendritic cells are acutely susceptible to infection with F. tularensis, but fail to produce pro-inflammatory cytokines or undergo maturation. Further, virulent F. tularensis actively interferes with the ability of human DC to respond to secondary stimuli. Understanding the mechanism by which F. tularensis actively suppresses DC function is a central directive of my laboratory. We are tackling this directive in two different ways. First, we are analyzing the role Francisella lipids play in mediating anti-inflammatory responses. Structures present on the surface of bacteria are the first components encountered by the host cell. Thus, it is possible that, in the context of F. tularensis infections, these structures contribute to the early, rapid suppression of human dendritic cells. Bacterial lipids represent one such structure. Preliminary evidence in our lab suggests that lipids associated with the outer membrane of F. tularensis can potently suppress inflammatory responses in human dendritic cells. We are currently identifying the specific lipid(s) responsible for this suppression and the mechanism by which they interfere with human dendritic cell functions. Second, we are exploring the intracellular host pathways modulated by F. tularensis, which negatively regulates human dendritic cells through multiple pathways. For example, if the replication of extracellular bacteria is restricted, the ability of human dendritic cells to produce TNF-alpha in response to other microbial stimuli is restored. However, a similar restoration of IL-12 production is not observed. We have demonstrated that rapid induction of IFN-beta by F. tularensis potently suppresses production of IL-12 in human dendritic cells. We are currently dissecting the specific pathways and molecular mechanisms by which IFN-beta modulates host responses in F. tularensis infected human dendritic cells. In addition to aiding in the development of novel vaccines and therapeutics, identification of bacterial products capable of negatively regulating specific host pathways (while leaving others intact) may provide new targets for therapeutics directed against cancer and autoimmune diseases. Finally, activation of the host cell inflammasome and subsequent secretion of the inflammatory cytokines IL-1beta and IL-18 is thought to be a central feature of host defense against a wide range of pathogens. Indeed, it has been shown that attenuated strains of F. tularensis are capable of activating the inflammasome resulting in cel death and release of IL-1b. However, our data suggests that virulent F. tularensis evades and interferes with this process. Currently, we are examining the role of the inflammasome, IL-1b and IL-18 in defense against tularemia. Additionally, our gaol is to determine how virulent F. tularensis disrupts this process.