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Ammonia inhibits phagosome-lysosome fusion in macrophages
Abstract:
When foreign bodies, including many microorganisms, are ingested by cultured macrophages, they become enclosed in phagosomes, with which lysosomes usually fuse and then discharge their enzymes and other contents into the resulting phagolysosomes. Such fusion is, however, diminished or absent after the phagocytosis of some pathogens, notably Mycobacterium tuberculosis and Toxoplasma gondii. Assuming that the nonfusion is due to active inhibition by the intrapoagosomal microbe, identification of an inhibitor should clarify the lysosomal control mechanism. It has been suggested that strongly acidic sulphatides present in virulent tuberculosis, which, like other substances with polyanionic structural features, can themselves block phagosome-lysosome fusion (P-LF), may contribute to the negative lysosome response to ingested tubercle bacilli. We report here another possibility, based on inhibition of fusion of yeast-containing phagosomes by filtrates from cultures of tubercle bacilli on traditional-type defined media; we show that the ammonia content of such filtrates is sufficient to account for their effect. This inhibition of fusion seems to be an hitherto unrecognized intracellular consequence of added ammonia, in striking contrast to the enhancement produced by some lipophilic amines.
Insights
Mycobacterium tuberculosis can prevent phagosome-lysosome fusion in macrophages. Ammonia in tubercle bacilli cultures inhibits this fusion, offering a new insight into pathogen evasion mechanisms.
Area of Science:
- Cellular biology
- Immunology
- Microbiology
Background:
- Macrophages engulf foreign bodies into phagosomes, which normally fuse with lysosomes for degradation.
- Some pathogens, like Mycobacterium tuberculosis, evade this process, inhibiting phagosome-lysosome fusion (P-LF).
- Acidic sulphatides in M. tuberculosis were previously suggested to cause P-LF.
Purpose of the Study:
- To investigate alternative mechanisms by which M. tuberculosis inhibits phagosome-lysosome fusion.
- To identify potential inhibitors released by M. tuberculosis during culture.
Main Methods:
- Culturing Mycobacterium tuberculosis on defined media.
- Preparing filtrates from these cultures.
- Assessing the effect of filtrates on yeast-containing phagosome-lysosome fusion in cultured macrophages.
- Analyzing the chemical composition of the filtrates, specifically ammonia content.
Main Results:
- Filtrates from M. tuberculosis cultures inhibited phagosome-lysosome fusion.
- The ammonia content of these filtrates was sufficient to account for the observed inhibition.
- This represents a newly recognized intracellular consequence of ammonia.
Conclusions:
- Ammonia produced by M. tuberculosis can actively inhibit phagosome-lysosome fusion.
- This mechanism offers a novel explanation for how M. tuberculosis evades macrophage antimicrobial defenses.
- Understanding this process could inform new therapeutic strategies against tuberculosis.