title: Rapid and complete fusion of macrophage lysosomes with phagosomes containing Salmonella typhimurium.
abstract: The virulence of Salmonella typhimurium for mice results, in part, from its ability to survive after phagocytosis by macrophages. Although it is generally agreed that intracellular bacteria persist in membrane-bound phagosomes, there remains some question as to whether these phagosomes fuse with macrophage lysosomes. This report describes the maturation of phagosomes containing S. typhimurium inside mouse bone marrow-derived macrophages. Macrophages were infected briefly and incubated for various intervals; then they were examined by fluorescence microscopy for colocalization of bacteria with lysosomal markers. These markers included LAMP-1, cathepsin L, and fluorescent proteins or dextrans preloaded into lysosomes by endocytosis. By all measures, phagosomes containing S. typhimurium merged completely with the lysosomal compartment within 20 min of phagocytosis. The rate of phagosome-lysosome fusion was similar to the rate for phagocytosed latex beads. Phagolysosomes remained accessible to fluid-phase probes and contained lysosomal markers for many hours. Moreover, a large percentage of the wild-type bacteria that were viable 20 min after infection survived longer incubations inside macrophages, indicating that the survivors were not a minor subpopulation that avoided phagosome-lysosome fusion. Therefore, we conclude that S. typhimurium survives within the lysosomal compartments of macrophages.
authors: Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors: Y K
authors: YK
authors: Oh
authors: C
authors: C
authors: Alpuche-Aranda
authors: E
authors: E
authors: Berthiaume
authors: T
authors: T
authors: Jinks
authors: S I
authors: SI
authors: Miller
authors: J A
authors: JA
authors: Swanson
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D056668:Cathepsin L; D002403:Cathepsins / Q000378:metabolism; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases; D010450:Endopeptidases; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D051907:Lysosomal Membrane Proteins; D008247:Lysosomes / Q000502:physiology*; D008264:Macrophages / Q000382:microbiology* / Q000648:ultrastructure; D008561:Membrane Fusion; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D010587:Phagocytosis; D010588:Phagosomes / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000276:immunology*; D013997:Time Factors
chemical_list: D015703:Antigens, CD; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D056668:Cathepsin L; C534278:Ctsl protein, mouse