title: Analysis of the Relative Contribution of Phagocytosis, LC3-Associated Phagocytosis, and Canonical Autophagy During Helicobacter pylori Infection of Macrophages.
abstract: BACKGROUND
  Previous findings have suggested that Helicobacter pylori induces autophagic processes and subsequently takes refuge in autophagosomes, thereby contributing to persistent infection. Recently, a noncanonical form of autophagy, LC3 (microtubule-associated protein 1 light chain 3)-associated phagocytosis (LAP), has been shown to be required for efficient clearance of some intracellular bacteria. Whether H. pylori infection induces LAP had not been examined previously. In this study, we determined the extent to which H. pylori infection induces canonical autophagy or LAP in macrophages, and the involvement of the H. pylori cag pathogenicity island (cagPAI) with these processes.
  
  
  METHODS
  Immunofluorescence confocal microscopy was used to analyze the formation of GFP-LC3 puncta and their colocalization with H. pylori. Transmission electron microscopy was used to detect the ultrastructure of H. pylori-containing compartments.
  
  
  RESULTS
  The majority of intracellular bacteria (85-95%) were found in phagosomes that were LC3-negative, with a small proportion (4-14%) appearing "free" in the cytosol. Only a very small percentage (0.5-6%) of intracellular H. pylori was sequestered in autophagosomes. Furthermore, no statistically significant difference in the relative distribution of H. pylori in the various compartments was observed between wild-type and cagPAI-mutant bacteria.
  
  
  CONCLUSIONS
  In macrophages, H. pylori infection does not induce LAP, but can induce canonical autophagy, which entraps a very small fraction of intracellular bacteria. We propose that this subpopulation of intracellular H. pylori might have escaped from phagosomes into the cytosol before being sequestered by autophagosomes. The cagPAI of H. pylori has only minor influence, if any, on the extent of these processes.
authors: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Vic., Australia.
authors: Nadia S
authors: NS
authors: Deen
authors: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Vic., Australia.
authors: Lan
authors: L
authors: Gong
authors: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Vic., Australia.
authors: Thomas
authors: T
authors: Naderer
authors: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Vic., Australia.
authors: Rodney J
authors: RJ
authors: Devenish
authors: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Vic., Australia.|Department of Microbiology, Monash University, Clayton, Vic., Australia.
authors: Terry
authors: T
authors: Kwok
mesh_terms: D000818:Animals; D001343:Autophagy; D002478:Cells, Cultured; D049452:Green Fluorescent Proteins / Q000032:analysis; D016480:Helicobacter pylori / Q000276:immunology*; D054884:Host-Pathogen Interactions; D006801:Humans; D008264:Macrophages / Q000382:microbiology* / Q000502:physiology*; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000032:analysis*; D010587:Phagocytosis; D013194:Staining and Labeling
chemical_list: C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D049452:Green Fluorescent Proteins
keywords: Helicobacter pylori; LC3-associated phagocytosis (LAP); autophagosomes; autophagy; macrophages; phagocytosis