INFLUENCE OF PNEUMOCYSTIS-CARINII ON NITRITE PRODUCTION BY RAT ALVEOLAR MACROPHAGES

Nitrite production by rat alveolar macrophages was studied to determin e the role of L-arginine oxidation in the interaction between these ce lls and Pneumocystis carinii. Alveolar macrophages from rats obtained from two different breeders were used: rats from Janvier breeder had l atent P. carinii infection, while those from Charles River breeder wer e bred in a germ-free environment. Pneumocystis carinii increased in v itro nitrite generation by unstimulated alveolar macrophages from Janv ier rats only, and this was blocked by N-G-monomethyl-L-arginine. Incu bation of cells from Janvier and Charles River rats with lipopolysacch aride and/or interferon-gamma increased nitrite production to a simila r extent. Pneumocystis carinii partially decreased nitrite release by activated alveolar macrophages, and this was still inhibited by N-G-mo nomethyl-L-arginine. In the presence of P. carinii, superoxide dismuta se used as a superoxide anion scavenger had no effect on nitrite produ ction by activated cells. These results show that prior exposure to P. carinii lends to nitric oxide production by rat alveolar macrophages. Although the magnitude of this production seems to be moderate, it is of biological significance since cells of P. carinii-naive rats do no t generate nitrite whereas those of latently infected rats do.