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Oxidants augment endotoxin-induced activation of alveolar macrophages
Abstract:
Endotoxin (lipopolysaccharide) stimulation of macrophages (M phi) induces the generation of toxic reactive oxygen intermediates (ROI); however, recent studies implicate intracellular redox changes in signal transduction pathways for cytokines. To test whether oxidant stress modulates M phi activation, rabbit alveolar M phi were exposed to the following: diamide (oxidizes intracellular glutathione); glucose oxidase (generates hydrogen peroxide); or xanthine oxidase (generates superoxide), before lipopolysaccharide. Supernatants were assayed for tumor necrosis factor (TNF) and cell lysates were assayed for procoagulant activity (PCA). TNF mRNA was analyzed by Northern blot. M phi exposure to diamide and glucose oxidase augmented TNF production, PCA expression, and TNF mRNA accumulation; however, xanthine oxidase exposure inhibited TNF production while augmenting PCA expression. M phi signal transduction can be enhanced by increasing cellular oxidant stress. The differential response of TNF versus PCA suggests the existence of distinct redox-sensitive signal transduction pathways. These data define a mechanism by which oxidants generated during inflammation may modulate M phi function.
Insights
Oxidant stress can enhance macrophage activation and cytokine production. Different reactive oxygen species differentially affect tumor necrosis factor and procoagulant activity, suggesting distinct redox-sensitive pathways in macrophages.
Area of Science:
- Immunology
- Cellular Biology
- Biochemistry
Background:
- Macrophages (M phi) produce toxic reactive oxygen intermediates (ROI) upon endotoxin stimulation.
- Intracellular redox changes are implicated in signaling pathways for cytokine production.
Purpose of the Study:
- To investigate if oxidant stress modulates macrophage activation.
- To determine the effects of specific oxidants on macrophage function.
Main Methods:
- Rabbit alveolar macrophages were exposed to diamide, glucose oxidase, or xanthine oxidase prior to lipopolysaccharide stimulation.
- Assays were performed for tumor necrosis factor (TNF) production, procoagulant activity (PCA), and TNF mRNA levels.
Main Results:
- Diamide and glucose oxidase augmented TNF production, PCA expression, and TNF mRNA.
- Xanthine oxidase inhibited TNF production but increased PCA expression.
- Macrophage signal transduction can be enhanced by increased cellular oxidant stress.
Conclusions:
- Distinct redox-sensitive signaling pathways exist for TNF and PCA in macrophages.
- Oxidants generated during inflammation may modulate macrophage function through these pathways.