Prevention of phagosome-lysosome fusion in cultured macrophages by sulfatides of Mycobacterium tuberculosis.

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Abstract
Intracellular parasites (e.g., Mycobacterium tuberculosis, Toxoplasma gondii, and some Chlamydiae) may promote their survival within the host by acting from within phagosomes to prevent phagolysosome formation, thus avoiding exposure to the lysosomal hydrolases. The present studies demonstrate that when sulfatides of M. tuberculosis (anionic trehalose glycolipids largely responsible for the neutral red reactivity of virulent strains) are administered to cultured mouse peritoneal macrophages, they accumulate in the secondary lysosomes, which are rendered incompetent for fusion with phagosomes containing suitable target particles such as viable yeasts. This antifusion effect is also exhibited when small amounts of sulfatide are introduced directly into phagosomes by attachment to the target yeasts prior to their ingestion. The sulfatides evidently exert a selective inhibitory influence on membrane fusion, analogous to what occurs typically when macrophage cultures are infected with tubercle bacilli. This effect may be due to ionic interaction between the polyanionic micelles of bacterial sulfatide and organelle membranes, modifying the latter and inducing dysfunction.