Manipulation of Host Innate Immunity by Listeria

微生物发病机制的一个核心问题是免疫系统细胞如何整合多种信号以诱导适当的反应以及病原体如何避免和/或操纵宿主反应。单核细胞增生李斯特菌是一种高度可处理的模型细胞内病原体，用它来解决这个问题。利用野生型和突变型缺乏分泌孔形成溶血酶（LLO）的细菌，研究人员发现了导致宿主基因表达的两种不同途径：以toll样受体信号传导为特征的空泡途径和以干扰素β (IFNb)产生为特征的细胞质途径。IFNb的表达至少部分是由最近发现的SecA2通路分泌的单胞乳杆菌自溶素（p60和NamA）介导的。看起来好像单核增生乳杆菌在操纵宿主系统

A central problem in microbial pathogenesis is how cells of the immune system integrate multiple signals to induce an appropriate response and how pathogens avoid and/or manipulate the host response. Listeria monocytogenes as a highly tractable model intracellular pathogen with which to approach this problem. Using wild-type and mutant bacteria lacking a secreted pore-forming hemolyisn (LLO), two separate pathways were discovered leading to host gene expression: a vacuolar pathway characterized by Toll-like Receptor signaling and a cytosolic pathway characterized by Interferon beta (IFNb) production. IFNb expression was mediated, at least in part, by L. monocyogenes autolysins (p60 and NamA) secreted by the recently discovered SecA2 pathway. It appeas as though L. monocytogenes is manipulating a host system of innate immunity by the production of a specific peptidoglycan (PGN) cleavage product. In Aim I, the macrophage transcriptional response to vacuolar and cytosolic bacteria will be determned using wildtype L. mononcytogenes and LLO-minus mutants in combination with B. subtilis or B. subtilis expressing LLO. Using macrophages isolated from mice lacking the IFNabR, MyD88, or TLR2, a panel of genes representing the vacuolar and cytosolic signaling will be established. In Aim II, the bacterial autolysins affecting macrophage signaling will be determined by introduction of in-frame deletions and characteization of the resulting mutants in mice and macrophages from wild-type and NOD1 and NOD2 knockouts. In Aim III, the contribution of specific PGN fragments will be determined using reverse phase high pressure liquid chromatography and mass spectrometry combined with introduction of purified PGN fragments into cells using liposomes with and without LLO. In Aim IV, activated peritoneal macrophages will be used to test the hypothesis will be tested that the cytosolic pathway actually detects material (PGN) derived from a vacuolar compartment resulting from degradation in a phagosome. In the final aim, the composite transcriptional 3rogram induced by L. monocytogenes will be compared with that induced by M. tuberculosis, F. tularensis and H. capsulatum.