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Effects of bafilomycin A1 on functional capabilities of LPS-activated alveolar macrophages
1Department of Internal Medicine, University of Texas Medical Branch, Galveston 77555-0561.
Abstract:
Resident alveolar macrophages (m phi) possess plasmalemmal vacuolar-type H(+)-ATPase (V-ATPase) that plays a crucial role in regulation of intracellular pH (pHi). To assess the importance of this V-ATPase to m phi effector functions, resident alveolar m phi from rabbits were activated with E. coli-derived lipopolysaccharide (LPS) and exposed to bafilomycin A1, a specific inhibitor of V-ATPase. Bafilomycin caused a significant cytosolic acidification in both the absence and presence of CO2-HCO3-, and in both unstimulated and activated m phi. Superoxide production and Fc receptor-mediated phagocytosis also were reduced in bafilomycin-treated m phi. Similar effects were elicited by acidifying the cytoplasm in the absence of bafilomycin, by lowering extracellular pH (pHo) from 7.4 to 6.5-6.6. Thus, the effects of bafilomycin on phagocytosis and superoxide production probably were related to cytosolic acidification, secondary to blockade of V-ATPase-mediated H+ extrusion across the plasma membrane. Conversely, bafilomycin significantly increased TNF-alpha release. This effect cannot be explained by a bafilomycin-induced acidosis because acidic pHo significantly reduced TNF-alpha release. The results demonstrate that V-ATPase activity is an important determinant of the effector functions of LPS-activated m phi.
Insights
Resident alveolar macrophages utilize vacuolar-type H(+)-ATPase (V-ATPase) for pH regulation. Inhibiting V-ATPase impairs macrophage phagocytosis and superoxide production but enhances TNF-alpha release, highlighting its role in effector functions.
Area of Science:
- Immunology
- Cell Biology
- Physiology
Background:
- Resident alveolar macrophages are key immune cells in the lungs.
- Intracellular pH (pHi) regulation is critical for macrophage function.
- Vacuolar-type H(+)-ATPase (V-ATPase) is present on the macrophage plasma membrane and involved in pHi control.
Purpose of the Study:
- To investigate the role of plasmalemmal V-ATPase in regulating macrophage effector functions.
- To determine the impact of V-ATPase inhibition on macrophage activation and cytokine release.
Main Methods:
- Alveolar macrophages were isolated from rabbits.
- Macrophages were activated with lipopolysaccharide (LPS).
- V-ATPase was inhibited using bafilomycin A1, and effects on pHi, superoxide production, phagocytosis, and TNF-alpha release were measured.
Main Results:
- Bafilomycin A1 treatment caused significant cytosolic acidification in macrophages.
- Inhibition of V-ATPase reduced superoxide production and Fc receptor-mediated phagocytosis.
- Conversely, bafilomycin A1 significantly increased TNF-alpha release.
Conclusions:
- Plasmalemmal V-ATPase activity is crucial for regulating effector functions in LPS-activated macrophages.
- Cytosolic acidification, secondary to V-ATPase blockade, likely underlies the observed reductions in phagocytosis and superoxide production.
- V-ATPase plays a complex role, influencing both pro-inflammatory and phagocytic activities of macrophages.