DISTINCT SIGNAL-TRANSDUCTION PATHWAYS FOR ACTIVATION OF RABBIT ALVEOLAR MACROPHAGES IN-VITRO BY COTTON BRACT TANNIN

These experiments were designed to study signal transduction pathways in alveolar macrophages stimulated by condensed tannin or zymosan. Con densed tannins, present in cotton mill dust, alter the host-defense fu nction of alveolar macrophages and may contribute to the pathogenesis of byssinosis. We tried to determine the early steps in signal transdu ction mechanisms of cell activation by tannin. With the quantification of Cr-51 release, we determined that tannin was cytotoxic for the cel ls after 30 min activation with 130 mu g for 2 x 10(6) cells. Cr-51 re lease was similar for control cells and zymosan- or 30 mu g tannin-act ivated cells. Using the luciferine luciferase reaction, we showed that tannin markedly depleted ATP cell content. In inositol-labeled cells, tannin increased inositolphosphate release in a dose-dependent manner . In lysoPAF-labeled cells, tannin induced synthesis of phosphatidic a cid and diglycerides. In the presence of ethanol, the level of tannin- induced phosphatidic acid was slightly reduced, and phosphatidylethano l was synthesized. No phosphatidylethanol was found in alveolar macrop hages stimulated by zymosan in the presence of ethanol. GF 109203X, a specific inhibitor of protein kinase C decreased only tannin-induced p hosphatidylethanol synthesis. In conclusion, tannin (at 30 or 130 mu g /ml) activated an inositol phospholipase C in alveolar membranes. Phos phatidylcholine phospholipases C and D were found only at the higher c oncentration of tannin. (C) 1996 Academic Press, Inc.