Determining the Mechanism of TNF in Defense Against Intracellular Bacterial Infection

项目摘要 细胞内细菌病原体，如嗜肺军团菌（Legionella pneumophila），其是军团病的病原体， 每年都给美国带来巨大的疾病负担。成功控制这些 病原体依赖于炎性细胞因子肿瘤坏死因子（TNF）。TNF负责 上调先天免疫活性，并指导炎症反应。靶向TNF的治疗剂 信号传导在治疗炎性疾病如类风湿性关节炎或溃疡性结肠炎中是常见的; 然而，这些治疗剂具有对细胞内细菌感染增加的易感性。TNF 已经证明是防御军团菌和其他细胞内病原体的关键因素， TNF信号传导的细节得到了很好的表征。然而，TNF的下游效应是多种多样的 从促进细胞存活到触发程序性细胞死亡， TNF介导的抗细菌防御仍然不清楚。 我们新的初步数据表明，在军团菌感染后，TNF是最佳的免疫调节所必需的。 骨髓衍生巨噬细胞（BMDM）培养物中炎性细胞因子产生。的机制 在军团菌感染期间TNF促进细胞因子产生的机制尚不清楚。此外，我们提出了新的 另外的数据显示，缺乏凋亡半胱天冬酶（Caspase-8）的小鼠和细胞具有以下缺陷： 外源性rTNF治疗不能挽救的军团菌感染的控制，表明TNF 下游机制可能与诱导感染宿主细胞凋亡有关。 因此，目的1试图检验促存活和炎症信号传导用于上调 受感染细胞产生保护性细胞因子。目的2试图检验TNF依赖性 受感染细胞中的凋亡信号传导作用于限制细菌的复制生态位，从而限制生长， 传播.这项研究将为TNF如何介导细胞内免疫控制提供基本的见解。 细菌感染，并可能提供一个基础，为发展改进的治疗方法， 病理性炎症而不增加感染的风险。

Project Summary Intracellular bacterial pathogens such as Legionella pneumophila, the causative agent of Legionnaires’ Disease, are responsible for significant disease burden in the United States every year. Successful control of these pathogens is reliant on the inflammatory cytokine Tumor Necrosis Factor (TNF). TNF is responsible for the upregulation of innate immune activity, and directs the inflammatory response. Therapeutics targeting TNF signaling are common in treatment of inflammatory disorders such as rheumatoid arthritis or ulcerative colitis; however, these therapeutics carry with them an increased susceptibility to intracellular bacterial infection. TNF has proven a critical factor in defense against Legionella and other intracellular pathogens, and the molecular details of TNF signaling are well characterized. The downstream effects of TNF, however, are diverse – ranging from promoting cell survival to triggering programmed cell death – and thus the precise mechanisms through which TNF mediates anti-bacterial defense are still unclear. Our new preliminary data indicate that, upon Legionella infection, TNF is required for optimal inflammatory cytokine production in bone marrow-derived macrophage (BMDM) culture. The mechanism by which TNF promotes cytokine production during Legionella infection is unknown. Furthermore, we present new additional data showing that mice and cells deficient for the apoptotic caspase, Caspase-8, possess a defect in control of Legionella infection that cannot be rescued by exogenous rTNF treatment, suggesting that TNF’s downstream mechanism may be related to the induction of apoptosis of infected host cells. Thus, Aim 1 seeks to test the hypothesis that pro-survival and inflammatory signaling serves to upregulate the production of protective cytokines by infected cells. Aim 2 seeks to test the hypothesis that TNF-dependent apoptotic signaling in infected cells acts to restrict the replicative niche of the bacteria and thus limit growth and spread. This research will provide fundamental insight into how TNF mediates immune control of intracellular bacterial infection, and may provide a basis for the development of improved therapeutics that dampen pathological inflammation without increased risk of infection.