NITRIC-OXIDE PRODUCTION - A MECHANISM OF CHLAMYDIA-TRACHOMATIS INHIBITION IN INTERFERON-GAMMA-TREATED RAW264.7 CELLS

IFN-gamma and/or LPS induced nitrite production and inhibition of Chla mydia trachomatis (CT) replication in the murine macrophage cell line, RAW264.7. Linear regression analysis demonstrated a strong correlatio n between nitrite production and inhibition of CT replication (correla tion coefficients: -0.93, P < 0.001). L-NMMA specifically inhibited ni trite production and restored CT replication (55-71%). Inducible nitri c oxide synthase (iNOS) mRNA was analyzed by Northern and dot blot hyb ridization with an iNOS cDNA probe. A strong correlation between iNOS mRNA expression and inhibition of CT replication also was observed (co rrelation coefficient: -0.97, P < 0.05). Furthermore, anti-TNF-alpha a ntibody, which completely neutralized biological activity of the secre ted TNF-alpha, neither inhibited nitrite production nor restored CT re plication in the LPS- and/or IFN-gamma-treated RAW264.7 cells. In mous e peritoneal macrophages treated with IFN-gamma, both L-NMMA and anti- TNF-alpha antibody inhibited nitrite production and restored CT replic ation. However, L-NMMA and the antibody had no effect upon nitrite pro duction and CT inhibition in LPS-treated peritoneal macrophages. These data indicate that NO production is one mechanism for inhibition of C T replication in IFN-gamma-activated murine macrophages.