Nitrite production by macrophages derived from BCG-resistant and -susceptible congenic mouse strains in response to IFN-gamma and infection with BCG.

Reactive nitrogen intermediates (RNI) have been implicated in the interferon-gamma (IFN-gamma)-induced anti-microbial action of macrophages against a wide variety of pathogens. We have been studying the production of NO2- by macrophage lines derived from the bone marrow of either B10.A (Bcgs) strain mice (B10S cell lines), or their congenic BCG-resistant partners of the B10A.Bcgr (Bcgr) strain (B10R cell lines). We have discovered that there is a significant difference in the production of NO2- of B10S compared with B10R macrophages in response to IFN-gamma. By 48 hr following treatment with 10 U/ml IFN-gamma, B10R macrophages had produced an approximately threefold higher level of NO2- than B10S macrophages. Similar results were obtained when experiments were performed with total splenic cells harvested from the spleens of B10.A.Bcgr and B10.A strain mice. The bacteriostatic activity, as assessed by the [3H]uracil incorporation by Mycobacterium bovis BCG, was higher in B10R macrophages compared to B10S macrophages. The bacteriostatic activity of B10R and B10S macrophages correlated with the amount of nitric oxide produced by the macrophages. The anti-mycobacterial activity was inhibited by NgMMLA, a specific inhibitor of nitrite and nitrate synthesis from L-arginine. Addition of L-arginine to IFN-gamma-stimulated macrophages in the presence of NgMMLA restored nitrite production and bacteriostatic activity of macrophages. Northern blot analysis of macrophage nitric oxide synthase (iNOS) revealed that the difference in NO2- production by IFN-gamma-treated B10S and B10R lines was reflective of the difference in iNOS mRNA expression.