Modulation of macrophage lysosomal pH by Mycobacterium tuberculosis-derived proteins

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Abstract
Macrophage lysosomal pH was significantly (greater than 1 pH unit) increased in a reversible, concentration-dependent manner characterized by a saturable and cyclic kinetics after exposure to culture filtrate protein extract derived from Mycobacterium tuberculosis. Lysosomal alkalinization peaked 30 min after administration of culture filtrate protein extract to cells of the macrophagelike cell line J774A.1. The alkalinization was reversible, and a second peak was observed approximately 60 min after incubation. Maximum lysosomal alkalinization increased as a function of culture filtrate protein extract concentration, reaching an apparent saturation level around 700 to 1,000 micrograms/ml, although the time course for this process was not significantly dependent on antigen concentration. The alkalinizing agent(s) was heat labile and produced a similar effect in cells which had a different lysosomal enzyme composition. Our observations are consistent with the presence of one or more mycobacterial antigens which have a pH-dependent affinity for lysosomal structures essential for lysosomal acidification and which are able to inhibit this lysosomal acidification.