Evaluation of nitric oxide production by Leishmania infantum-infected dog macrophages

Protozoa of the genus Leishmania (L.) infect reticuloendothelial cells of several mammalian species, including dogs, in which they often give rise to a chronic, not self-healing visceral disease. Since the parasitocidal mechanism of macrophages towards Leishmania in dog has not yet been well investigated, in this work we have evaluated in Leishmania infantum-infected macrophage cultures from 10 healthy dogs, killing capacity and nitric oxide (NO) production, in terms of nitrite (NO2) levels. Parallel experiments were performed on macrophages stimulated with both Concanavalin A (ConA)-activated PBMC supernatants and Salmonella typhimurium lipopolysaccharide (LPS), and in the same conditions, but in the presence of the NO synthase inhibitor L-N monomethylarginine (L-NMMA). In L. infantum-infected macrophages, nitric oxide production was observed at a concentration significantly higher after stimulation with both Con A-activated PBMC supernatants and LPS than that observed in uninfected cells cultured in medium alone, or infected cells unstimulated or stimulated by PBMC supernatants or LPS alone, respectively. Moreover, NO production was abolished in the presence of the NO synthase inhibitor L-NMMA. Finally, killing of Leishmania by macrophages was significantly reduced in the presence of L-NMM