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Evidence for pH sensitivity of tumor necrosis factor-alpha release by alveolar macrophages
A Bidani1, C Z Wang, S J Saggi
1Department of Internal Medicine, Shriners Burns Institute, University of Texas Medical Branch, Galveston 77555-0561, USA.
Abstract:
Alveolar macrophages (m phi) participate in inflammatory and immune responses in acidic microenvironments such as the interstitial fluids of tumors and abscesses. Two plasmalemmal H+ extruders interact to control the acid-base status of alveolar m phi, namely a V-type H+ pump (V-ATPase) and a Na+/H+ exchanger. The present study examined the effects of extracellular pH (pHo) and H+ transport inhibitors on tumor necrosis factor-alpha (TNF-alpha) release induced by endotoxin (lipopolysaccharide) in rabbit alveolar m phi. The amount and activity of TNF-alpha in m phi-conditioned media were determined by enzyme-linked immunosorbent assay and L929 fibroblast bioassay, respectively. TNF-alpha release was suppressed progressively at lower pHo values (< or = 7.0). Also, bafilomycin A1 (a specific inhibitor of V-ATPases) significantly reduced the amount and activity of TNF-alpha in m phi-conditioned media (pHo 7.4). However, bafilomycin caused a significant increase in the nonspecific cytotoxicity (i.e. bioactivity insensitive to TNF-alpha antibody) of m phi-conditioned media. The effects of bafilomycin specifically on TNF-alpha release followed a time course similar to that of acidic pHo, suggesting that both treatments acted on similar events in the lipopolysaccharide signal transduction pathway. Amiloride (an inhibitor of Na+ transporters including the Na+/H+ exchanger) also suppressed TNF-alpha release but displayed a time course of action different from the acidic pHo or bafilomycin.
Insights
Acidic environments and V-type H+ pump inhibitors reduce tumor necrosis factor-alpha (TNF-alpha) release from alveolar macrophages. These findings suggest shared pathways in lipopolysaccharide signaling.
Area of Science:
- Immunology
- Cell Biology
- Physiology
Background:
- Alveolar macrophages (m phi) are crucial immune cells involved in inflammatory responses.
- Acidic microenvironments, found in tumors and abscesses, can influence immune cell function.
- Alveolar m phi utilize V-type H+ pumps and Na+/H+ exchangers to regulate intracellular pH.
Purpose of the Study:
- To investigate the impact of extracellular pH (pHo) and H+ transport inhibitors on TNF-alpha release from rabbit alveolar m phi stimulated by lipopolysaccharide (LPS).
Main Methods:
- Alveolar m phi were stimulated with LPS.
- TNF-alpha levels and activity were measured using ELISA and L929 fibroblast bioassay.
- The effects of varying pHo, bafilomycin A1 (V-ATPase inhibitor), and amiloride (Na+/H+ exchanger inhibitor) were assessed.
Main Results:
- TNF-alpha release was progressively inhibited at lower pHo values (<= 7.0).
- Bafilomycin A1 significantly reduced TNF-alpha release and activity at pHo 7.4, suggesting V-ATPase involvement in TNF-alpha production.
- Amiloride also suppressed TNF-alpha release, indicating a role for Na+/H+ exchangers.
Conclusions:
- Both acidic extracellular pH and V-ATPase inhibition suppress TNF-alpha release, implying convergence on LPS signal transduction pathways.
- Na+/H+ exchangers also play a role in regulating TNF-alpha release, though potentially through distinct mechanisms.