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Effect of interferon-gamma on the 5-lipoxygenase pathway of rat lung macrophages
N Meslier1, A J Aldrich, T D Bigby
1Cardiovascular Research Institute, University of California, San Francisco.
Abstract:
In view of conflicting reports concerning the effect of macrophage activation on arachidonic acid metabolism, we examined the effect of the macrophage activator, interferon-gamma (IFN-gamma), on the 5-lipoxygenase pathway in rat lung macrophages. Rat lung macrophages were conditioned in the presence or absence of 10(2) U/ml IFN-gamma for 4 h before stimulation with 1 microM A23187 for 15 min or 100 micrograms/ml opsonized zymosan for 60 min at 37 degrees C as well as other stimuli. Lipoxygenase products in extracted cell supernatants were identified and analyzed by high-pressure liquid chromatography and ultraviolet spectroscopy. The predominant lipoxygenase products included leukotriene (LT) B4, LTC4, and 5-hydroxyeicosatetraenoic acid (5-HETE). These products were not qualitatively altered by conditioning with IFN-gamma. However, 5-lipoxygenase pathway activity, as measured by LTB4 release, was maximally increased 2-fold after conditioning with IFN-gamma and stimulating with either A23187 or opsonized zymosan. IFN-gamma-conditioned macrophages, stimulated with A23187, released greater quantities of lipoxygenase products in comparison with control cells (307.6 +/- 13.3 versus 167.6 +/- 3.9 pmol LTB4/10(6) cells) (mean +/- SEM) (P less than 0.05). Similar results were obtained with the less potent stimulus, opsonized zymosan. IFN-gamma had no direct stimulatory effect on the 5-lipoxygenase pathway. No effect was observed with a variety of other stimuli with or without IFN-gamma conditioning.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Interferon-gamma (IFN-gamma) significantly enhances macrophage 5-lipoxygenase pathway activity, increasing leukotriene B4 release. This activation boosts inflammatory mediator production without altering product types.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophage activation's role in arachidonic acid metabolism is debated.
- Interferon-gamma (IFN-gamma) is a key macrophage activator.
- The 5-lipoxygenase pathway is crucial for inflammatory mediator synthesis.
Purpose of the Study:
- To investigate the effect of IFN-gamma on the 5-lipoxygenase pathway in rat lung macrophages.
- To determine how IFN-gamma influences the production of lipoxygenase products.
- To clarify conflicting reports on macrophage activation and arachidonic acid metabolism.
Main Methods:
- Rat lung macrophages were conditioned with IFN-gamma.
- Cells were stimulated with A23187 or opsonized zymosan.
- Lipoxygenase products were analyzed using high-pressure liquid chromatography and ultraviolet spectroscopy.
Main Results:
- IFN-gamma conditioning maximally increased 5-lipoxygenase pathway activity (LTB4 release) up to 2-fold.
- IFN-gamma-conditioned macrophages released significantly greater quantities of lipoxygenase products (e.g., LTB4) compared to controls.
- Product profiles (LTB4, LTC4, 5-HETE) were qualitatively unchanged by IFN-gamma.
Conclusions:
- IFN-gamma enhances macrophage 5-lipoxygenase pathway activity, particularly LTB4 production.
- This enhancement increases the release of inflammatory mediators without altering their types.
- IFN-gamma does not directly stimulate the pathway but potentiates responses to other stimuli.