Intracellular Growth of Mycobacterium Avium in Macrophages: Consequences on Membrane Traffic and Exchange of Contents between Endosomes, Lysosomes and Phagosomes

Macrophages represent major effector cells in the defense against a wide variety of microorganisms. However, several pathogens, such as mycobacteria (d’Arcy Hart 1982), Legionella pneumophila (Horwitz 1983),Toxoplasma gondii (Jones and Hirsch 1972), resist to the microbicidal activity of macrophages by blocking phagosome-lysosome fusions. Among the non tuberculous mycobacteria, M. avium emerges as a major pathogen in AIDS patients (Young et al. 1986). This organism survives within in vitro grown bone marrow-derived macrophages, remaining confined to the phagosome compartment in which it multiplies (Ryter et al. 1984). It resists to the hydrolytic activity of macrophages by inhibiting phagosome-lysosome (P-L) fusions (Frehel et al. 1986a) and thanks to its capsule that seems to reduce the diffusion of lysosomal enzymes (Frehel et al. 1986b).