title: On the killing of mycobacteria by macrophages.
abstract: Both pathogenic and non-pathogenic mycobacteria are internalized into macrophage phagosomes. Whereas the non-pathogenic types are invariably killed by all macrophages, the pathogens generally survive and grow. Here, we addressed the survival, production of nitrogen intermediates (RNI) and intracellular trafficking of the non-pathogenic Mycobacterium smegmatis, the pathogen-like, BCG and the pathogenic M. bovis in different mouse, human and bovine macrophages. The bacteriocidal effects of RNI were restricted for all bacterial species to the early stages of infection. EM analysis showed clearly that all the mycobacteria remained within phagosomes even at late times of infection. The fraction of BCG and M. bovis found in mature phagolysosomes rarely exceeded 10% of total, irrespective of whether bacteria were growing, latent or being killed, with little correlation between the extent of phagosome maturation and the degree of killing. Theoretical modelling of our data identified two different potential sets of explanations that are consistent with our results. The model we favour is one in which a small but significant fraction of BCG is killed in an early phagosome, then maturation of a small fraction of phagosomes with both live and killed bacteria, followed by extremely rapid killing and digestion of the bacteria in phago-lysosomes.
authors.affiliation: Molecular Pathogenesis Centre, Unit of Retrovirus and Associated Infections, Faculty of Pharmacy, University of Lisbon, Av. Forcas Armadas, 1600-083 Lisbon, Portugal.
authors.forename: Luisa
authors.initials: L
authors.lastname: Jordao
authors.forename: Christopher K E
authors.initials: CK
authors.lastname: Bleck
authors.forename: Luis
authors.initials: L
authors.lastname: Mayorga
authors.forename: Gareth
authors.initials: G
authors.lastname: Griffiths
authors.forename: Elsa
authors.initials: E
authors.lastname: Anes
mesh_terms: D000818:Animals; D002417:Cattle; D049452:Green Fluorescent Proteins / Q000032:analysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008247:Lysosomes / Q000382:microbiology / Q000648:ultrastructure; D008264:Macrophages / Q000382:microbiology* / Q000502:physiology; D051379:Mice; D018448:Models, Immunological; D009163:Mycobacterium bovis / Q000276:immunology*; D020102:Mycobacterium smegmatis / Q000276:immunology*; D009569:Nitric Oxide / Q000096:biosynthesis; D019001:Nitric Oxide Synthase / Q000502:physiology; D052247:Nitric Oxide Synthase Type II / Q000032:analysis / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D010588:Phagosomes / Q000382:microbiology / Q000648:ultrastructure
chemical_list: D049452:Green Fluorescent Proteins; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D009584:Nitrogen