title: Analysis of cells targeted by Salmonella type III secretion in vivo.
abstract: The type III secretion systems (TTSS) encoded in Salmonella pathogenicity island-1 and -2 (SPI-1 and -2) are virulence factors required for specific phases of Salmonella infection in animal hosts. However, the host cell types targeted by the TTSS have not been determined. To investigate this, we have constructed translational fusions between the beta-lactamase reporter and a broad array of TTSS effectors secreted via SPI-1, SPI-2, or both. Secretion of the fusion protein to a host cell was determined by cleavage of a specific fluorescent substrate. In cultured cells, secretion of all six effectors could be observed. However, two to four days following i.p. infection of mice, only effectors secreted by SPI-2 were detected in spleen cells. The cells targeted were identified via staining with nine different cell surface markers followed by FACS analysis as well as by conventional cytological methods. The targeted cells include B and T lymphocytes, neutrophils, monocytes, and dendritic cells, but not mature macrophages. To further investigate replication in these various cell types, Salmonella derivatives were constructed that express a red fluorescent protein. Bacteria could be seen in each of the cell types above; however, most viable bacteria were present in neutrophils. We find that Salmonella is capable of targeting most phagocytic and non-phagocytic cells in the spleen but has a surprisingly high preference for neutrophils. These findings suggest that Salmonella specifically target splenic neutrophils presumably to attenuate their microbicidal functions, thereby promoting intracellular survival and replication in the mouse.
authors.affiliation: Department of Microbiology and Immunology, Oregon Health and Science University, Portland, Oregon, United States of America.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Geddes
authors.forename: Frank
authors.initials: F
authors.lastname: Cruz
authors.forename: Fred
authors.initials: F
authors.lastname: Heffron
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D005434:Flow Cytometry; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006367:HeLa Cells; D006801:Humans; D016131:Lymphocyte Subsets / Q000382:microbiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009504:Neutrophils / Q000382:microbiology; D011993:Recombinant Fusion Proteins; D012481:Salmonella Infections, Animal / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D013154:Spleen / Q000166:cytology / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; C440638:SPI-2 protein, Salmonella; C419942:Spi1 protein, Salmonella