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Enhancing effect of oxygen radical scavengers on murine macrophage anticryptococcal activity through production of
M Tohyama1, K Kawakami, M Futenma
1First Department of Internal Medicine, Faculty of Medicine, University of the Ryukyus, Okinawa, Japan.
Abstract:
We examined the roles of reactive nitrogen intermediates (RNI) and reactive oxygen intermediates (ROI) in interferon-gamma (IFN-gamma)-induced cryptococcostatic activity of murine peritoneal macrophages using N(G)-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of RNI synthesis, and superoxide dismutase (SOD) and catalase, oxygen radical scavengers. IFN-gamma-activated macrophages produced nitric oxide (NO) in a dose-dependent manner, as measured by increased nitrite concentration 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 microM L-NMMA. These results confirmed the importance of the RNI-mediated effector mechanism in anticryptococcal activity of macrophages. SOD and catalase significantly enhanced the cryptococcostatic activity of macrophages induced by a suboptimal dose of IFN-gamma (20 U/ml). The augmenting effect of these reagents was mediated by NO, since they potentiated the production of NO by macrophages and their effects were totally blocked by L-NMMA. Our results indicate that the IFN-gamma-induced anticryptococcal activity of macrophages is dependent mostly on RNI, and suggest that the ROI system down-regulates the effector mechanism for cryptococcostasis by suppressing the RNI system.
Insights
Interferon-gamma (IFN-gamma) activates macrophages to fight Cryptococcus, primarily through reactive nitrogen intermediates (RNI). Reactive oxygen intermediates (ROI) appear to suppress this RNI-mediated antifungal activity.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Interferon-gamma (IFN-gamma) is crucial for macrophage-mediated immunity.
- The roles of reactive nitrogen intermediates (RNI) and reactive oxygen intermediates (ROI) in macrophage antifungal activity are not fully understood.
Purpose of the Study:
- To investigate the specific contributions of RNI and ROI in IFN-gamma-induced cryptococcostatic activity of murine peritoneal macrophages.
- To elucidate the interplay between RNI and ROI in macrophage-mediated defense against Cryptococcus.
Main Methods:
- Utilized N(G)-monomethyl-L-arginine (L-NMMA), an RNI synthesis inhibitor.
- Employed superoxide dismutase (SOD) and catalase, ROI scavengers.
- Quantified nitric oxide (NO) production via nitrite concentration.
- Assessed cryptococcal growth inhibition in macrophage cultures.
Main Results:
- IFN-gamma induced dose-dependent nitric oxide (NO) production and enhanced cryptococcostatic activity.
- L-NMMA significantly suppressed IFN-gamma-induced killing activity and NO production.
- SOD and catalase augmented the cryptococcostatic effect of suboptimal IFN-gamma doses, mediated by NO and blocked by L-NMMA.
Conclusions:
- IFN-gamma-induced anticryptococcal activity of macrophages is predominantly mediated by RNI.
- The ROI system may down-regulate macrophage effector mechanisms by suppressing RNI production.