Salmonella-Induced Cytopathology in Human Macrophages

The goal of this research project is to define the bacterial virulence factors and macrophage host responses underlying serious, disseminated Salmonella infection. Non-typhoid Salmonella are common causes of food born illness, disseminated infection causes substantial morbidity and mortality. Our understanding of how Salmonella produces extra-intestinal disease is limited. <P> This project focuses on the host-pathogen interaction between human macrophages and the protein products of 2 major Salmonella loci: the spv locus, a critical virulence determinant of dissemination, and the Salmonella Pathogenicity Island, SPI-2. The spv operon encodes SpvB protein, an ADPribosyl transferase, which modifies actin monomers. SPI-2 encodes a bacterial type III secretion system specifically active when Salmonella are intracellular. <P> The specific aims are: 1) To define bacterial virulence genes required for Salmonella-induced cytotoxicity in human macrophages. 2) To analyse the mechanisms bacterial effectors use to induce this cytopathology, including apoptosis. 3) To determine the Toll-like receptor (TLR) signaling and effect on Mitogen Activated Protein Kinase (MAPK) pathways when macrophages phagocytose Salmonella<P> The hypothesis is that on phagocytosis, Salmonella lipopolysaccaride (LPS) triggers a TLR-4 mediated cell signaling pathway, stimulating p38 MAPK, causing initial inhibition of apoptosis. This allows time for the organism to proliferate, intracellularly. SpvB secretion then breaks down cellular actin, and programmed cell death is initiated. This triggers cell surface localization markers, for phagocytosis by other uninfected macrophages, facillitating Salmonella spread. <P> My long term objective is to gain a full-time academic appointment to conduct independent research on molecular genetic mechanisms pathogens have evolved to over come macrophages innate immune responses. <P> The project outlined, guided by mentors at UCSD and supplemented by graduate courses, will provide training in bacterial molecular genetics, signal transduction analysis, and apoptsis in macrophages.