Salmonella protein AvrA promotes survival and dissemination within the host

描述（由申请人提供）：传染性鼠伤寒沙门氏菌血清型是美国重大的健康负担，估计每年有7600万例食源性疾病和5000例相关死亡。沙门氏菌引起的急性肠炎临床表现为严重痉挛和分泌性腹泻，是美国最常见的感染性肠胃炎病因。某些沙门氏菌菌株在宿主细胞内建立自己而没有外部疾病迹象，因为它们已经进化出复杂的机制来逃避宿主的先天免疫。许多受感染的患者成为慢性病原体携带者，并在最初侵袭和急性肠胃炎后的很长一段时间内继续通过粪便和尿液排出沙门氏菌。这些患者是主要的公共卫生问题，因为他们是病原体宿主。大量文献致力于鉴定促进沙门氏菌在宿主内存活、传播和持续存在的候选分子。我们之前的研究表明，一些沙门氏菌菌株分泌预先形成的AvrA效应蛋白，能有效抑制先天免疫JNK和NF-kB信号通路，从而在感染侵袭阶段阻断细胞因子的产生、中性粒细胞的募集和细胞凋亡的激活。然而，AvrA在宿主中介导沙门氏菌传播和持久性的功能尚未得到解决，这将是本提案的重点。有趣的初步数据表明，在果蝇动物模型中，AvrA的同时表达和细胞因子的刺激可以促进免疫细胞的增殖。我们假设AvrA对先天免疫通路的扭曲负责，影响沙门氏菌的传播和/或慢性持久性。我们拟在1)表达AvrA的非复制腺病毒感染的原代骨髓源性白细胞和2)小鼠沙门氏菌感染模型中研究AvrA介导的细胞增殖机制。在这两个目标中，我们将使用细胞特异性标记和FACS分析来识别增殖的白细胞亚群。作为这项研究的结果，我们将推进目前对细菌在传播或慢性携带者状态下生存策略的了解。

DESCRIPTION (provided by applicant): Infectious Salmonella typhimurium serovars are a substantial health burden in the United States with an estimated 76 million cases of food borne illness and 5,000 associated deaths annually. Acute enteritis caused by Salmonella strains is manifested clinically by severe cramping and secretory diarrhea, and is the most common cause of infectious gastroenteritis in the United States. Certain Salmonella strains establish themselves within the host cells with no outward signs of disease because they have evolved sophisticated mechanisms to evade host innate immunity. Many infected patients become chronic pathogen carriers and continue to shed Salmonella in stools and urine for prolonged periods following initial invasion and acute gastroenteritis. These patients are a major public health concern because they are pathogen reservoirs. An extensive body of literature is devoted to identifying candidate molecules facilitating Salmonella survival, dissemination and persistence within the host. We have previously shown that some Salmonella strains secrete the preformed AvrA effector protein that potently inhibits the innate immune JNK and NF-kB signaling pathways, thus blocking cytokine production, neutrophil recruitment, and activation of apoptosis during the invasion stage of infection. However, the function of AvrA in mediating Salmonella dissemination and persistence within the host not been addressed, and will be the focus of this proposal. Intriguing preliminary data presented here demonstrate that concurrent AvrA expression and cytokine stimulation force proliferation of immune cells within the Drosophila animal model. We hypothesis that AvrA is responsible for skewing innate immune pathways, influencing Salmonella dissemination and/or chronic persistence. We propose to examine the mechanisms of AvrA mediated cell proliferation in 1) primary bone marrow derived leukocytes infected with nonreplicating adenovirus expressing AvrA, and 2) a murine salmonellosis infection model. In both aims, we will identify the proliferating leukocyte sub-sets using cell specific markers and FACS analysis. As an outcome of the study, we will advance current knowledge of bacterial strategies for survival during dissemination or in the chronic carrier state. PUBLIC HEALTH RELEVANCE: The research is significant because it will contribute to a full understanding of the evasion strategies evolved by enteric pathogens to escape the immune response and persist within the host. The positive impact of this study on advancing our knowledge of host/pathogen interactions will have relevance in human disease, allowing better understanding and potential treatment for chronic Salmonella infection.