Role of inorganic nitrogen oxides and tumor necrosis factor alpha in killing Leishmania donovani amastigotes in gamma interferon-lipopolysaccharide-activated macrophages from Lshs and Lshr congenic mouse strains

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Abstract
The capacity of mature bone-marrow-derived macrophages and resident peritoneal macrophages from Lshr versus Lshs congenic mice to kill intracellular Leishmania donovani amastigotes when activated by recombinant gamma interferon-lipopolysaccharide (rIFN-gamma-LPS) was examined. IFN-gamma alone in doses up to 100 U/ml was unable to activate macrophages to kill L. donovani amastigotes in vitro; LPS was a necessary secondary stimulus. Similarly, LPS alone in doses up to 100 ng/ml produced no leishmanicidal activity. In bone marrow macrophages, a dose-dependent increase in leishmanicidal activity was observed as increasing rIFN-gamma-LPS dose combinations were introduced, with Lshr macrophages maintaining a significant but not dramatic advantage within any particular dose combination. For peritoneal macrophages, the reverse was true, with macrophages from Lshs mice being more efficient at killing for doses of LPS up to 10 ng/ml with doses of rIFN-gamma in the range of 11 to 33 U/ml. The degree of killing in both bone marrow and peritoneal macrophages correlated well with the levels of nitrites measured in the supernatants at 72 h, and a highly significant correlation was observed between 4-, 24-, or 72-h tumor necrosis factor alpha (TNF-alpha) release and nitrite production measured at 72 h. Inclusion of 200 microM NG-monomethyl-L-arginine, a competitive inhibitor of the L-arginine-dependent pathway for the synthesis of inorganic nitrogen oxides, inhibited the killing, as did the addition of neutralizing anti-TNF-alpha antibody. These results are consistent with previous data showing an important autocrine role for TNF-alpha in enhancing production of inorganic nitrogen oxides by primed or activated macrophages. In addition, our results suggest that production of TNF-alpha and nitrites after priming or activation signals may be under a different regulatory control in mature bone marrow macrophages than in the resident peritoneal macrophage population.