Inducible nitric oxide synthase and nitric oxide production in Leishmania infantum-infected human macrophages stimulated with interferon-gamma and bacterial lipopolysaccharide

Nitric oxide produced by an inducible nitric oxide synthase constitutes one of the main microbicidal mechanisms of murine macrophages and its importan ce is now being recognized for human macrophages. In this study we evaluate d inducible nitric oxide synthase expression, nitric oxide release, and par asitocidal ability of Leishmania infantum-infected monocyte-derived human m acrophages. The inducible nitric oxide synthase was detected by immunofluor escence and western blotting and nitric oxide production was measured by th e Griess reaction for nitrites. Parasite killing was microscopically evalua ted by fluorescent dyes. Experiments were performed on macrophages with or without previous stimulation with recombinant human interferon-y and bacter ial lipopolysaccharide. Inducible nitric oxide synthase expression and nitr ic oxide release were higher in Leishmania-infected stimulated macrophages than in uninfected cells or infected cells without previous stimulation. Ni tric oxide production and parasitocidal activity against Leishmania infantu m were reduced in macrophages treated with the nitric oxide synthase inhibi tor L-N-G monomethylarginine. These results suggest a microbicidal role for nitric oxide in human leishmaniasis, with the possible practical applicati on of immunological or pharmacological regulation of nitric oxide synthesis in the treatment of this infection.