Project summary Intracellular bacteria, most notably, Salmonella enterica and Mycobacterium tuberculosis, infect hundreds of millions of people and cause millions of deaths annually. These pathogens can establish chronic infections to survive long-term within host tissues. In chronic stage, many infected individuals are asymptomatic, but they can progress to develop active disease. Currently there is a paucity of effective strategies to monitor and modulate disease progression, reactivation risks, and therapy responsiveness for chronic bacterial infections. A key pathological feature common to many intracellular bacterial infections is granuloma, a complex and dynamic tissue microstructure comprised of immune cells, particularly macrophages, and pathogens. Granuloma formation is thought to be an important immune response to control infection, but it also serves as a crucial mechanism for pathogen persistence. Our long-term goal is to identify common pathways involved in granuloma formation that would lead to fundamental advances in diagnostic and therapeutic modalities for chronic bacterial infections. In the current proposal, we will take multipronged approaches to dissect mechanisms of host- pathogen interactions underpinning granuloma formation and control of chronic Salmonella infection. In Aim 1, we will define the mechanisms by which a critical host factor regulates granuloma formation and bacterial persistence. The objective of Aim 2 is to identify the key pathways of granuloma formation manipulated by a novel Salmonella virulence factor. In Aim 3, we propose to construct an innovative reporter system consisting of genetically engineered mice and genetically engineered Salmonella to characterize development and maintenance of granuloma macrophages. The proposed research is a component of a mentored career development plan for the candidate to acquire a unique interdisciplinary skillset to achieve an independent academic research career studying host-pathogen interactions in the pathogenesis of bacterial infections. The candidate is currently an Instructor in the Division of Pediatric Infectious Diseases, Department of Pediatrics, at Stanford University. The proposed research draws upon the candidate’s experience in cellular immunology, bacterial pathogenesis, and clinical infectious diseases. Together with planned didactics and technical training, the experiments outlined will provide the candidate a framework to acquire new domains of expertise including molecular microbiology and bacterial genetics, cutting- edge mammalian genetic manipulation techniques, and computational and systems immunology represented by his primary mentor, Dr. Denise Monack, and a team of leading physician-scientist advisors.