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The effects of eosinophil-granule major basic protein on lung-macrophage superoxide anion generation
J A Rankin1, P Harris, S J Ackerman
1Research Service, West Haven Veterans Hospital, CT 06516.
Abstract:
The effects of major basic protein (MBP) on superoxide anion release in vitro from normal guinea pig (GP) alveolar macrophages (AM) was determined. Native MBP at 55 micrograms/ml had an immediate effect (reduction) on phorbol myristate acetate (PMA)-induced (p less than 0.01) and spontaneous (p = 0.055) superoxide (O2-) release by GP AMs. A similar effect was not observed from AMs incubated for 24 hours with MBP before assessment of O2- release. However, after AMs were incubated with MBP for 48 hours, again there was a significant reduction observed in both PMA-induced (p = 0.01) and spontaneous (p = 0.002) O2- release compared to that of control cultures. The immediate effect of MBP on AM O2- release was not due to cytotoxicity of MBP for AM. In contrast, the effect observed after 48 hours of culture was due, in part, to a direct toxic effect of the MBP on the AM because the viability of AM cultured for 48 hours with MBP (55 micrograms/ml) was 63.6% +/- 13% compared to the viability of control cultures of AM that was 83.9% +/- 7%; p = 0.03. The effect of MBP on AM O2- release at 48 hours was progressive over concentrations ranging from 2 to 55 micrograms/ml. These data suggest that native MBP can affect adversely PMA-induced and spontaneous release of O2- by GP AMs and that this effect depends only in part on the cytotoxic properties of MBP.
Insights
Major Basic Protein (MBP) immediately reduces superoxide release from guinea pig alveolar macrophages (AMs). However, prolonged exposure to MBP causes cytotoxicity, contributing to reduced superoxide release.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Alveolar macrophages (AMs) play a crucial role in innate immunity.
- Superoxide anion (O2-) release is a key function of AMs in response to stimuli.
- Major Basic Protein (MBP) is a cationic protein found in eosinophils, known for its inflammatory properties.
Purpose of the Study:
- To investigate the effects of native Major Basic Protein (MBP) on superoxide anion (O2-) release from guinea pig (GP) alveolar macrophages (AMs) in vitro.
- To determine if MBP's effects are immediate or require prolonged incubation.
- To assess the role of cytotoxicity in MBP's impact on AM function.
Main Methods:
- Primary guinea pig alveolar macrophages (AMs) were isolated.
- Superoxide anion (O2-) release was measured following stimulation with phorbol myristate acetate (PMA) and spontaneously.
- AMs were treated with varying concentrations of native MBP for different incubation periods (immediate, 24 hours, 48 hours).
- Cell viability was assessed to determine cytotoxicity.
Main Results:
- Native MBP (55 µg/ml) immediately reduced both PMA-induced and spontaneous O2- release by GP AMs (p < 0.01).
- No significant effect was observed after 24 hours of incubation.
- After 48 hours of incubation, MBP significantly reduced both PMA-induced (p = 0.01) and spontaneous (p = 0.002) O2- release.
- The immediate effect was not cytotoxic, but the 48-hour effect was partly due to MBP-induced cytotoxicity (viability reduced from 83.9% to 63.6%, p = 0.03).
- The inhibitory effect at 48 hours showed a dose-dependent relationship with MBP concentrations from 2 to 55 µg/ml.
Conclusions:
- Native MBP can adversely affect both PMA-induced and spontaneous superoxide anion release by guinea pig alveolar macrophages.
- The mechanism of MBP's effect is concentration-dependent and time-dependent.
- While immediate exposure inhibits O2- release without cytotoxicity, prolonged exposure leads to inhibition partly mediated by direct toxic effects on AMs.
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