A Mammalian Cellular Niche for Chronic Bacteria

描述(由申请人提供)：尽管在了解急性细菌性疾病的机制方面取得了很大进展，但慢性病涉及的机制--在其他健康的宿主中持续存在--远不为人所知。慢性细菌感染是一个主要的公共卫生问题，因为受感染的人看起来很健康，但往往会排出细菌，导致急性感染的爆发或流行。使用慢性细菌感染的小鼠模型，我们发现沙门氏菌存在于一种特殊的巨噬细胞中，即吞噬细胞的巨噬细胞，这种巨噬细胞吞噬了活的白细胞。这些巨噬细胞类似于伤寒患者体内携带沙门氏菌的巨噬细胞，被称为“伤寒细胞”。我们现在想要确定使细菌能够在吞噬细胞的巨噬细胞内生存的分子机制。为此，我们开发了一种体内观察的组织培养模型，该模型概括了细菌在巨噬细胞内的复制，巨噬细胞摄取了实验室中生长的活的但不是死亡的白细胞。在这个高度集中的提案中，我们概述了三个问题，我们将利用这一模型来确定持续感染的分子机制。1)当细菌在吞噬活的白细胞的巨噬细胞内复制时，它们是空泡的还是胞质的？活的白细胞和/或鼠伤寒沙门氏菌做出了哪些贡献，使细菌能够复制？巨噬细胞的激活状态是否因摄入活的白细胞和/或细菌而改变，从而允许细菌复制？这些研究将为允许细菌在吞噬细胞巨噬细胞中复制的信号通路的分子分析奠定基础。这项建议与公共卫生有关，因为它解决了一个鲜为人知的重大医学意义的问题：细菌在慢性感染期间如何以及在哪里生存。一旦这些问题得到解决，就可以开发清除慢性细菌感染的治疗方法，降低急性细菌感染的流行频率/严重程度。

DESCRIPTION (provided by applicant): Despite great strides in understanding the mechanisms of acute bacterial disease, the mechanisms involved in chronic disease - persistence in an otherwise healthy host - are far less known. Chronic bacterial infections are a major public health problem because infected individuals appear healthy, but often shed bacteria, causing outbreaks or epidemics of acute infection. Using a mouse model of chronic bacterial infection, we have discovered that salmonellae reside within a particular kind of macrophage, cytophagocytic macrophages, that have ingested live white blood cells. These are similar to macrophages that can harbor salmonellae in humans with typhoid fever and that are referred to as "typhoidal cells". We now want to identify the molecular mechanisms that enable the bacteria to survive within cytophagocytic macrophages. To this end, we developed a tissue culture model of our in vivo observations which recapitulates the replication of bacteria inside of macrophages that have ingested live, but not dead, white blood cells grown in the laboratory. In this highly focused proposal we outline 3 questions with which we will exploit this model to identify the molecular mechanisms of persistent infection. 1.) Are bacteria vacuolar or cytosolic when they replicate within macrophages that have ingested live white blood cells? 2.) What contributions do the live white blood cells and/or S. typhimurium make that allow the bacteria to replicate? 3.) Is the activation state of macrophages altered by the ingestion of live white blood cells and/or bacteria to allow for bacterial replication? These studies will lay the foundation for molecular analyses of the signaling pathways that allow for bacterial replication in cytophagocytic macrophages. This proposal is relevant to public health because it addresses a poorly understood issue of major medical importance: how and where do bacteria survive during chronic infection. Once these questions have been addressed, therapeutics that clear chronic bacterial infections can be developed, reducing the frequency/severity of epidemics of acute bacterial infection.