Evidence for pH Sensitivity of Tumor Necrosis
Factor- Release by Alveolar Macrophages
A. Bidani, C. Z. Wang, S. J. Saggi, and T. A. Heming
Departments of Internal Medicine, and Physiology and Biophysics, and the Shriners Burns Institute,
University of Texas Medical Branch, Galveston, TX 77555-0561, USA
Abstract. Alveolar macrophages (m) 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, namely a V-type H
+
pump (V-ATPase) and a Na
+
/H
+
exchanger.
The present study examined the effects of extracellular pH (pH
o
) and H
+
transport
inhibitors on tumor necrosis factor- (TNF-) release induced by endotoxin (lipo-
polysaccharide) in rabbit alveolar m. The amount and activity of TNF- in m-
conditioned media were determined by enzyme-linked immunosorbent assay and
L929 fibroblast bioassay, respectively. TNF- release was suppressed progressively
at lower pH
o
values (7.0). Also, bafilomycin A
1
(a specific inhibitor of V-
ATPases) significantly reduced the amount and activity of TNF- in m-
conditioned media (pH
o
7.4). However, bafilomycin caused a significant increase in
the nonspecific cytotoxicity (i.e. bioactivity insensitive to TNF- antibody) of m-
conditioned media. The effects of bafilomycin specifically on TNF- release fol-
lowed a time course similar to that of acidic pH
o
, 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- release but displayed a time course of action different from the
acidic pH
o
or bafilomycin.
Key words: Cytokine—V-ATPase—Na
+
/H
+
exchange—Bafilomycin A
1
—
Amiloride.
Introduction
Tumor necrosis factor- (TNF-) is a pleiotropic cytokine produced by mononuclear
phagocytes in the setting of neoplastic and infectious diseases [11, 15, 19, 26]. It serves
Offprint requests to: Akhil Bidani, Pulmonary Division, Department of Internal Medicine, University
of Texas Medical Branch, Galveston, TX 77555-0561, USA
Lung (1998) 176:111–121
© Springer-Verlag
New York Inc. 1998