title: Characterization of the Mycobacterium tuberculosis phagosome and evidence that phagosomal maturation is inhibited.
abstract: We have used the cryosection immunogold technique to study the composition of the Mycobacterium tuberculosis phagosome. We have used quantitative immunogold staining to determine the distribution of several known markers of the endosomal-lysosomal pathway in human monocytes after ingestion of either M. tuberculosis, Legionella pneumophila, or polystyrene beads. Compared with the other phagocytic particles studied, the M. tuberculosis phagosome exhibits delayed clearance of major histocompatibility complex (MHC) class I molecules, relatively intense staining for MHC class II molecules and the endosomal marker transferrin receptor, and relatively weak staining for the lysosomal membrane glycoproteins, CD63, LAMP-1, and LAMP-2 and the lysosomal acid protease, cathepsin D. In contrast to M. tuberculosis, the L. pneumophila phagosome rapidly clears MHC class I molecules and excludes all endosomal-lysosomal markers studied. In contrast to both live M. tuberculosis and L. pneumophila phagosomes, phagosomes containing either polystyrene beads or heat-killed M. tuberculosis stain intensely for lysosomal membrane glycoproteins and cathepsin D. These findings suggest that (a) M. tuberculosis retards the maturation of its phagosome along the endosomal-lysosomal pathway and resides in a compartment with endosomal, as opposed to lysosomal, characteristics; and (b) the intraphagosomal pathway, i.e., the pathway followed by several intracellular parasites that inhibit phagosome-lysosome fusion, is heterogeneous.
authors: Department of Medicine, University of California, Los Angeles School of Medicine 90024.
authors: D L
authors: DL
authors: Clemens
authors: M A
authors: MA
authors: Horwitz
mesh_terms: D015703:Antigens, CD / Q000378:metabolism; D002451:Cell Compartmentation; D006684:HLA-DR Antigens / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007425:Intracellular Membranes; D016952:Legionella pneumophila / Q000472:pathogenicity; D051907:Lysosomal Membrane Proteins; D008247:Lysosomes / Q000502:physiology; D008561:Membrane Fusion; D008562:Membrane Glycoproteins / Q000378:metabolism; D009000:Monocytes / Q000382:microbiology*; D009169:Mycobacterium tuberculosis / Q000472:pathogenicity*; D010587:Phagocytosis; D010588:Phagosomes / Q000502:physiology / Q000648:ultrastructure*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D011990:Receptors, Transferrin / Q000378:metabolism; D060149:Tetraspanin 30; D001613:beta 2-Microglobulin / Q000378:metabolism
chemical_list: D015703:Antigens, CD; C554586:CD63 protein, human; D006684:HLA-DR Antigens; D015395:Histocompatibility Antigens Class I; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D010980:Platelet Membrane Glycoproteins; D011990:Receptors, Transferrin; D060149:Tetraspanin 30; D001613:beta 2-Microglobulin