Characterization of the Mycobacterium tuberculosis phagosome and evidence that phagosomal maturation is inhibited.

Abstract

SummaryWe 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-l, and LAMP-2 and the lysosomal acid protease, cathepsin D. In contrast to M. tuberculosis, the L. pneumophila phagosome rapidly dears MHC class I molecules and excludes all endosomal-lysosomal markers studied. In contrast to both live M. tuberculosis and L. pneumophih 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.

Arrest of Mycobacterial Phagosome Maturation Is Caused by a Block in Vesicle Fusion between Stages Controlled by rab5 and rab7

“…6D). The very low level of Lamp proteins observed on MPC compared with LBC was in agreement with the observations by Clemens and Horwitz (20). In the case of rab7, ECL analysis of such blots indicated 146.8 Ϯ 18.9 arbitrary units for LBC versus 15.8 Ϯ 6.3 arbitrary units for MPC.…”

“…Reports that M. tuberculosis resides in macrophage compartments that display limited fusion capacity with the lysosome have a relatively long history (15)(16)(17)(18)(19)(20)(21)(22)(23). A link has been postulated (13,15,18,21) between this intriguing phenomenon (15,16), or other potential pathways of intracellular survival (42), and the capacity of pathogenic mycobacteria to survive and replicate in host monocytes.…”

Human CD8+ CTL Specific for the Mycobacterial Major Secreted Antigen 85A

“…However, the means by which Ags, from a bacteria which has been shown to reside within the phagosome (a site inaccessible to the MHC class I presentation pathway) are presented to CD8 ϩ T cells is unclear (56,57). However, recent FIGURE 6.…”

Lipoprotein Access to MHC Class I Presentation During Infection of Murine Macrophages with Live Mycobacteria

“…Activation of macrophages by MHC class II-restricted CD4 ϩ T cells has a central role in this process (1). However, following infection of macrophages with Mycobacterium tuberculosis, Mycobacterium avium, or Mycobacterium bovis bacillus Calmette-Guérin (BCG), 3 the normal process of phagosomal maturation is delayed, allowing the live bacteria to persist within a nonacidified intracellular compartment that exhibits early endosomal properties (2)(3)(4)(5)(6). Since processing of Ags for MHC class II presentation occurs within acidic compartments (7), failure to progress down the phagolysosomal pathway may entail a delay in the CD4 ϩ T cell response to live mycobacteria.…”