ENHANCING EFFECT OF OXYGEN RADICAL SCAVENGERS ON MURINE MACROPHAGE ANTICRYPTOCOCCAL ACTIVITY THROUGH PRODUCTION OF NITRIC-OXIDE

We examined the roles of reactive nitrogen intermediates (RNI) and rea ctive oxygen intermediates (ROI) in interferon-gamma (IFN-gamma)-induc ed cryptococcostatic activity of murine peritoneal macrophages using N -G-monomethyl-L-arginine (r-NMMA), a competitive inhibitor of RNI synt hesis, and superoxide dismutase (SOD) and catalase, oxygen radical sca vengers. IFN-gamma-activated macrophages produced nitric oxide (NO) in a dose-dependent manner, as measured by increased nitrite concentrati on in the culture supernatant. IFN-gamma also enhanced the suppressive effect on cryptococcal growth in a similar dose-dependent manner. The induction of killing activity and NO production by an optimal dose of IFN-gamma(100 U/ml) was virtually suppressed by 500 mu M L-NMMA. Thes e results confirmed the importance of the RNI-mediated effector mechan ism in anticryptococcal activity of macrophages. SOD and catalase sign ificantly enhanced the cryptococcostatic activity of macrophages induc ed by a suboptimal dose of IFN-gamma (20 U/ml). The augmenting effect of these reagents was mediated by NO, since they potentiated the produ ction of NO by macrophages and their effects were totally blocked by L -NMMA. Our results indicate that the IFN-gamma-induced anticryptococca l activity of macrophages is dependent mostly on RNI, and suggest that the ROI system down-regulates the effector mechanism for cryptococcos tasis by suppressing the RNI system.