title: IL-10 produced by trophoblast cells inhibits phagosome maturation leading to profound intracellular proliferation of Salmonella enterica Typhimurium.
abstract: BACKGROUND
  Salmonella enterica Typhimurium (ST) is a phagosomal pathogen that can infect placental trophoblast cells leading to abortion and severe maternal illness. It is unclear how the trophoblast cells promote profound bacterial proliferation.
  
  
  METHODS
  The mechanism of internalization, intracellular growth and phagosomal biogenesis in ST-infected human epithelial (HeLa), macrophage (THP-1) and trophoblast-derived cell lines (JEG-3, BeWo and HTR-8) was studied. Specific inhibitors were used to block bacterial internalization. Phagosomal maturation was determined by confocal microscopy, Western-blotting and release of lysosomal β-galactosidase by infected cells. Bacterial colony forming units were determined by plating infected cell lysates on agar plates.
  
  
  RESULTS
  ST proliferated minimally in macrophages but replicated profoundly within trophoblast cells. The ST-ΔinvA (a mutant of Salmonella pathogenicity island-1 gene effector proteins) was unable to infect epithelial cells, but was internalized by scavenger receptors on trophoblasts and macrophages. However, ST was contrastingly localized in early (Rab5⁺) or late (LAMP1⁺) phagosomes within trophoblast cells and macrophages respectively. Furthermore trophoblast cells (unlike macrophages) did not exhibit phagoso-lysosomal fusion. ST-infected macrophages produced IL-6 whereas trophoblast cells produced IL-10. Neutralizing IL-10 in JEG-3 cells accelerated phagolysomal fusion and reduced proliferation of ST. Placental bacterial burden was curtailed in vivo in anti-IL-10 antibody treated and IL-10-deficient mice.
  
  
  CONCLUSIONS
  Macrophages phagocytose but curtail intracellular replication of ST in late phagosomes. In contrast, phagocytosis by trophoblast cells results in an inappropriate cytokine response and proliferation of ST in early phagosomes.
  
  
  CONCLUSIONS
  IL-10 production by trophoblast cells that delays phagosomal maturation may facilitate proliferation of pathogens in placental cells.
authors.affiliation: Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, ON, Canada.
authors.forename: T
authors.initials: T
authors.lastname: Nguyen
authors.forename: N
authors.initials: N
authors.lastname: Robinson
authors.forename: S E
authors.initials: SE
authors.lastname: Allison
authors.forename: B K
authors.initials: BK
authors.lastname: Coombes
authors.forename: S
authors.initials: S
authors.lastname: Sad
authors.forename: L
authors.initials: L
authors.lastname: Krishnan
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D015415:Biomarkers / Q000378:metabolism; D002460:Cell Line; D049109:Cell Proliferation; D015169:Colony Count, Microbial; D004847:Epithelial Cells / Q000276:immunology / Q000378:metabolism / Q000382:microbiology / Q000648:ultrastructure; D006801:Humans; D016753:Interleukin-10 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D052118:Lysosomal-Associated Membrane Protein 1 / Q000235:genetics / Q000378:metabolism; D008247:Lysosomes / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology / Q000648:ultrastructure; D008264:Macrophages / Q000276:immunology / Q000378:metabolism / Q000382:microbiology / Q000648:ultrastructure; D008561:Membrane Fusion; D050296:Microbial Viability; D009154:Mutation; D010587:Phagocytosis; D010588:Phagosomes / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology / Q000648:ultrastructure; D012486:Salmonella typhimurium / Q000254:growth & development* / Q000276:immunology / Q000378:metabolism / Q000648:ultrastructure; D014327:Trophoblasts / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology / Q000648:ultrastructure; D015854:Up-Regulation; D020696:rab5 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D015415:Biomarkers; C508609:IL10 protein, human; D052118:Lysosomal-Associated Membrane Protein 1; C419942:Spi1 protein, Salmonella; D016753:Interleukin-10; D020696:rab5 GTP-Binding Proteins
keywords: CFU; Immune response; Interleukin 10; LAMP-1; Phagosomal maturation; Pregnancy; SCV; SPI; ST; Salmonella Typhimurium; Salmonella containing vacuole; Salmonella enterica Typhimurium; Salmonella pathogenicity Island; TTSS; Trophoblast cells; Type III secretion system; colony forming unit; lysosomal activating membrane protein-1