Toxoplasma gondii partially inhibits nitric oxide production of activated murine macrophages

Activated macrophages produce nitric oxide (NO) and as such are able to control the multiplication of Toxoplasma gondii. Until now, no reports have described a possible modulation of NO production of macrophages after T. gondii infection. To investigate this possibility, murine blood monocyte-derived and peritoneal macrophages were activated in vitro with interferon-gamma and lipopolysaccharide and infected with T. gondii and Trypanosoma cruzi, and NO production was evaluated. NO was produced by monocyte-derived macrophages only if cultured in the presence of macrophage-colony-stimulating factor. Monocyte-derived or peritoneal macrophages infected with T. gondii presented a significant reduction in NO production. NO production inhibition was not detected after T. cruzi infection. Macrophages infected with higher T. gondii/macrophage ratios presented lower NO production. Furthermore, only viable T. gondii could cause partial inhibition of NO production. In macrophages activated 24 h before the interaction, partial inhibition was detected after 3 h of infection and continued for 48 h. In macrophages activated immediately after the interaction, partial inhibition was not detected at 12 h, but was observed at 24 h. T. gondii-infected macrophages present lower inducible nitric oxide synthase expression as assayed by immunofluorescence. T. gondii did not develop in monocyte-derived macrophages producing NO, but were not totally eliminated. These results demonstrate that T. gondii infection partially inhibits NO production by murine macrophages, suggesting that a deactivating macrophage mechanism may be used for better survival into phagocytic cells.