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Macrophage oxygen-dependent antimicrobial activity. II. The role of oxygen intermediates
Abstract:
The capacity of three populations of mouse peritoneal macrophages to generate oxidative metabolites (as judged by extracellular release of H2O2) was compared to their ability to influence the intracellular fate of virulent Toxoplasma gondii. Macrophages from normal mice released little H2O2 and allowed unrestricted multiplication of intracellular toxoplasmas. Cells from chronically infected, immune (IM) mice released 4 times more H2O2 and displayed microbistatic activity. In contrast, macrophages from immune-boosted (IB) mice released 25 times more H2O2 than normal cells and rapidly killed the bulk of ingested toxoplasmas within 1 h. When macrophage monolayers were exposed to scavengers of O2-, H2O2, OH., and 1O2, both the inhibition of intracellular toxoplasma multiplication by IM macrophages and the killing of toxoplasmas by IB macrophages were reversed. Depriving cells of glucose, which markedly reduced H2O2 release, resulted in similar reversal of IM and IB macrophage anti-toxoplasma activity. As judged by the effect of the individual oxygen intermediate scavengers, O2- and H2O2 appeared to serve as precursors for the key toxic agents which may include OH. and 1O2. Providing normal macrophages with an exogenous source of oxidative metabolites generated by xanthine and xanthine oxidase, but not glucose and glucose oxidase, resulted in inhibition of intracellular toxoplasma growth. These findings suggest the presence of an oxygen-dependent antimicrobial system in mononuclear phagocytes beyond the production of O2- and H2O2, and indicate an important role for oxygen intermediates in macrophage resistance to the intracellular pathogen T. gondii.
Insights
Mouse macrophages use oxidative metabolites to fight Toxoplasma gondii. Immune-boosted macrophages rapidly kill parasites, suggesting an oxygen-dependent antimicrobial system in macrophages.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Macrophages play a crucial role in host defense against intracellular pathogens.
- Oxidative metabolites produced by macrophages are implicated in antimicrobial activity.
- Toxoplasma gondii is an opportunistic intracellular parasite that infects macrophages.
Purpose of the Study:
- To compare the oxidative metabolite generation capacity of different mouse macrophage populations.
- To assess the correlation between oxidative metabolite production and intracellular parasite control.
- To elucidate the role of oxygen intermediates in macrophage resistance to Toxoplasma gondii.
Main Methods:
- Culturing mouse peritoneal macrophages from normal, chronically infected (IM), and immune-boosted (IB) mice.
- Measuring extracellular hydrogen peroxide (H2O2) release as an indicator of oxidative metabolite generation.
- Assessing the intracellular fate of virulent Toxoplasma gondii within macrophages.
- Utilizing scavengers of reactive oxygen species (ROS) and deprivation of glucose to investigate the role of oxidative intermediates.
- Exogenously supplying oxidative metabolites to normal macrophages.
Main Results:
- Normal macrophages produced minimal H2O2 and allowed unrestricted T. gondii multiplication.
- IM macrophages released significantly more H2O2 and exhibited microbistatic activity against T. gondii.
- IB macrophages released substantially higher levels of H2O2 and rapidly killed ingested T. gondii.
- Inhibition of oxidative intermediates reversed the anti-Toxoplasma activity of IM and IB macrophages.
- Exogenous oxidative metabolites inhibited T. gondii growth in normal macrophages.
Conclusions:
- Macrophage anti-Toxoplasma activity is dependent on oxidative metabolite generation.
- Oxygen intermediates, potentially including hydroxyl radicals (OH.) and singlet oxygen (1O2), are key toxic agents.
- Macrophages possess an oxygen-dependent antimicrobial system that extends beyond superoxide (O2-) and H2O2 production.
- Oxygen intermediates play a critical role in macrophage-mediated resistance to T. gondii infection.