The ability of pathogenic mycobacteria to block phagosome-lysosome fusion is critical for its pathogenesis. The molecules expressed by mycobacteria that inhibit phagosome maturation and the mechanism of this inhibition have been extensively studied. Recent work has indicated that mannosylated lipoarabinomannan (ManLAM) isolated from Mycobacterium tuberculosis can function to delay phagosome-lysosome fusion and that this delay requires the interaction of ManLAM with the mannose receptor (MR). However, the molecules expressed by other pathogenic mycobacteria that function to inhibit phagosome maturation have not been well described. In the present study, we show that phagosomes containing silica beads coated with glycopeptidolipids (GPLs), a major surface component of Mycobacterium avium, showed limited acidification and delayed recruitment of late endosomal/lysosomal markers compared to those of phosphatidylcholine-coated beads. The carbohydrate component of the GPLs was required, as beads coated only with the lipopeptide core failed to delay phagosome-lysosome fusion. Moreover, the ability of GPLs to delay phagosome maturation was dependent on the macrophage expression of the MR. Using CHO cells expressing the MR, we confirmed that the GPLs bind this receptor. Finally, human monocyte-derived macrophages knocked down for MR expression showed increased M. avium phagosome-lysosome fusion relative to control cells. Together, the data indicate that GPLs can function to delay phagosome-lysosome fusion and suggest that GPLs, like ManLAM, work through the MR to mediate this activity.Mycobacterium avium, a prominent opportunistic pathogen in AIDS patients and a source of pulmonary infections in non-AIDS patients, is an intracellular pathogen which resides primarily in host macrophages. Like most pathogenic mycobacteria, M. avium resides within a phagosome which fails to mature to a phagolysosome (22). Phagosomes containing viable M. avium retain early endosomal markers such as Rab5 and the transferrin receptor but lack complete luminal acidification and recruitment of late endosomal/lysosomal markers (7,14,27,28). The mechanism by which pathogenic mycobacteria are able to block phagosome-lysosome (P-L) fusion is of great interest, and how Mycobacterium tuberculosis performs this function has been extensively studied (27). Studies from Deretic and colleagues support that live M. tuberculosis blocks the normal calcium rise initiated upon a phagocytic response, the result of which leads to a diminished recruitment of type III phosphatidyl-inositol-3-kinase VPS34 to the phagosome, which limits phosphatidyl-inositol-3-phosphate (PI3P) formation and association of PI3P binding proteins such as early endosomal antigen 1 (EEA1) (8,26). The result is a loss in the tethering and fusion of late endosomes with the mycobacterial phagosome (8, 26).The M. tuberculosis surface-located mannosylated lipoarabinomannan (ManLAM) has been implicated in delaying P-L fusion. Published reports indicate that ManLAM can block the calcium influx re...