title: Macrophages rapidly transfer pathogens from lipid raft vacuoles to autophagosomes.
abstract: Macrophages activate autophagy as an immediate response to Legionella pneumophila infection, but what marks the pathogen phagosome as a target for the autophagy machinery is not known. Because a variety of bacteria, parasites, viruses, and toxins that associate with the endoplasmic reticulum enter host cells by a cholesterol-dependent route, we tested the hypothesis that autophagy is triggered when microbes engage components of lipid raft domains. As the intracellular respiratory pathogen L. pneumophila or the extracellular uropathogen FimH(+) Escherichia coli entered macrophages by a cholesterol-sensitive mechanism, they immediatezly resided in vacuoles rich in glycosylphosphatidylinositol moieties and the autophagy enzyme Atg7. As expected for autophagosomes, the vacuoles sequentially acquired the endoplasmic reticulum protein BiP, the autophagy markers Atg8 and monodansyl-cadaverine, and the lysosomal protein LAMP-1. A robust macrophage response to the pathogens was cholesterol-dependent, since fewer Atg7-rich vacuoles were observed when macrophages were pretreated with methyl-beta-cyclodextrin or filipin. A model in which macrophages exploit autophagy to capture pathogens within the lipid raft pathway for antigen presentation prior to disposal in lysosomes is discussed.
authors.affiliation: Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
authors.forename: Amal O
authors.initials: AO
authors.lastname: Amer
authors.forename: Brenda G
authors.initials: BG
authors.lastname: Byrne
authors.forename: Michele S
authors.initials: MS
authors.lastname: Swanson
mesh_terms: D000818:Animals; D001343:Autophagy / Q000187:drug effects / Q000502:physiology*; D000071193:Autophagy-Related Protein 7; D000071190:Autophagy-Related Protein 8 Family; D001427:Bacterial Toxins / Q000378:metabolism; D001854:Bone Marrow Cells / Q000166:cytology; D002784:Cholesterol / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D004927:Escherichia coli Infections / Q000382:microbiology; D016952:Legionella pneumophila / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000382:microbiology / Q000502:physiology*; D021962:Membrane Microdomains / Q000382:microbiology / Q000502:physiology*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010588:Phagosomes / Q000187:drug effects / Q000382:microbiology / Q000502:physiology*; D052899:Pore Forming Cytotoxic Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D014617:Vacuoles / Q000187:drug effects / Q000382:microbiology / Q000502:physiology*
chemical_list: C113757:ATG8 protein, S cerevisiae; C502661:Atg7 protein, mouse; D000071190:Autophagy-Related Protein 8 Family; D001427:Bacterial Toxins; D008869:Microtubule-Associated Proteins; D052899:Pore Forming Cytotoxic Proteins; D029701:Saccharomyces cerevisiae Proteins; C032676:aerolysin; D002784:Cholesterol; D000071193:Autophagy-Related Protein 7; D020123:Sirolimus