NITRIC OXIDE-INDEPENDENT KILLING OF FRANCISELLA-TULARENSIS BY IFN-GAMMA-STIMULATED MURINE ALVEOLAR MACROPHAGES

Alveolar macrophages (AMs) were analyzed for ability to support replic ation of the intracellular bacterium Francisella tularensis live vacci ne strain (LVS). AM supported in vitro growth (2 to 3 logs over 5 days ) of LVS with a doubling time of 8 +/- 0.8 h. AMs were analyzed for re sponsiveness to rIFN-gamma for destruction of this lung pathogen. AM t reated with 50 U/ml rIFN-gamma allowed early growth of bacteria (six d oublings over 48 h) but between 48 and 96 h rIFN-gamma-treated AM elim inated 1.5 logs of LVS. AMs were sensitive to effects of rIFN-gamma; a s little as 5 U/ml rIFN-gamma stimulated AM antimicrobial activity, wi th half-maximal activity 0.3 U/ml. rIFN-gamma-induced antimicrobial ef fects in AM correlated with amount of nitrites produced, but nitric ox ide played only a minimal role in antibacterial effects induced in AM, because N-G-MMLA (specific inhibitor of L-arginine-dependent nitric o xide production) failed to block antimicrobial activity of IFN-gamma-s timulated AM. IL-10, TGF-beta 1, and IFN-alpha (cytokines known to reg ulate effector functions of activated macrophages) also did not block anti-F. tularensis activity of IFN-gamma-stimulated AM. Reactive oxyge n metabolites, depletion of tryptophan, and sequestration of iron did not contribute to anti-F. tularensis activity because addition of supe roxide dismutase or catalase, excess iron, or tryptophan to IFN-gamma- treated AM did not reverse the anti-F. tularensis activity observed in these cells. Regulation of AM effector activity differed from that of other macrophage populations, in that while rIFN-gamma-stimulated AM produced TNF-alpha (100 U/ml at 72 h), TNF-alpha was not required as a costimulator for induction of antimicrobial activities by rIFN-gamma because anti-TNF-alpha treatment of rIFN-gamma-stimulated AM blocked T NF-alpha but had no effect on either production of nitrites or anti-F. tularensis activity.