Selective Mycobacterium avium–induced production of nitric oxide by human monocyte‐derived macrophages

Infection with a virulent strain of Mycobacterium avium , but not with virulent Mycobacterium tuberculosis or avirulent Mycobacterium smegmatis , induced the formation of nitric oxide by human monocyte‐derived macrophages. This process was not affected by lipopolysaccharide or cytokines such as interferon‐ γ or tumor necrosis factor α . M. avium‐induced nitric oxide production was significantly decreased by N G ‐monomethyl‐l‐arginine, a potent inhibitor of nitric oxide synthase activity, without any significant enhancement of intramacrophagic mycobacterial growth. Infection with all the three mycobacterial species induced a significant activation of phospholipase A 2 activity of macrophages as evidenced by the increased release of thromboxane A 2 . Finally, nitric oxide production by human monocyte‐derived macrophages required infection with live M. avium , as neither gamma‐irradiated M. avium nor the subcellular fractions of this microorganism (cell wall, cytosol) were able to trigger nitric oxide synthesis. J. Leukoc. Biol. 56: 36–40; 1994.