We studied the kinetics of in vivo nitrite production in the inflammatory reaction induced by M. bovis BCG into the pleural space. Pleural macrophages harvested from C57Bl/6 mice after acute BCG infection produced high levels of nitric oxide (NO). Enhanced production was obtained upon stimulation with LPS plus IFN-gamma. In sharp contrast, macrophages from DBA-2 mice produced low levels of NO, as nitrite, at the same time interval (24 h after BCG infection), being completely refractory to further stimulation. After the third day, NO production was similar in both strains. There was a close relationship between nitrite levels in the pleural exudate in vivo and those produced by harvested macrophages in vitro. In this in vivo system, the pattern of NO production by pleural macrophages one day after BCG infection was discrepant and unexpected in the response of C57Bl/6 and DBA-2 mice. However, this early response did not affect the late progressive NO production in both mice strains, that may be responsible to the late control of the mycobacteria growth.

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