EVIDENCE FOR PH SENSITIVITY OF TUMOR-NECROSIS-FACTOR-ALPHA RELEASE BYALVEOLAR MACROPHAGES

Alveolar macrophages (m phi) participate in inflammatory and immune re sponses in acidic microenvironments such as the interstitial fluids of tumors and abscesses. Two plasmalemmal H+ extruders interact to contr ol 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 (pH(o)) and H+ transport inhibitors on tumor necr osis factor-alpha (TNF-alpha) release induced by endotoxin (lipopolysa ccharide) in rabbit alveolar m phi. The amount and activity of TNF-alp ha in m phi-conditioned media were determined by enzyme-linked immunos orbent assay and L929 fibroblast bioassay, respectively. TNF-alpha rel ease was suppressed progressively at lower pH(o), values (less than or equal to 7.0). Also, bafilomycin A(l) (a specific inhibitor of V-ATPa ses) significantly reduced the amount and activity of TNF-alpha in m p hi-conditioned media (pH(o) 7.4). However, bafilomycin caused a signif icant increase in the nonspecific cytotoxicity (i.e. bioactivity insen sitive to TNF-alpha antibody) of m phi-conditioned media. The effects of bafilomycin specifically on TNF-alpha release followed a time cours e similar to that of acidic pH(o), suggesting that both treatments act ed on similar events in the lipopolysaccharide signal transduction pat hway. Amiloride (an inhibitor of Na+ transporters including the Na+/H exchanger) also suppressed TNF-alpha release but displayed a time cou rse of action different from the acidic pH(o) or bafilomycin.