Distinct Signal Transduction Pathways for Activation of Rabbit Alveolar Macrophagesin Vitroby Cotton Bract Tannin

Abstract

These experiments were designed to study signal transduction pathways in alveolar macrophages stimulated by condensed tannin or zymosan. Condensed tannins, present in cotton mill dust, alter the host-defense function of alveolar macrophages and may contribute to the pathogenesis of byssinosis. We tried to determine the early steps in signal transduction mechanisms of cell activation by tannin. With the quantification of51Cr release, we determined that tannin was cytotoxic for the cells after 30 min activation with 130 μg for 2 × 106cells.51Cr release was similar for control cells and zymosan- or 30 μg tannin-activated 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 acid and diglycerides. In the presence of ethanol, the level of tannin-induced phosphatidic acid was slightly reduced, and phosphatidylethanol was synthesized. No phosphatidylethanol was found in alveolar macrophages stimulated by zymosan in the presence of ethanol. GF 109203X, a specific inhibitor of protein kinase C decreased only tannin-induced phosphatidylethanol synthesis. In conclusion, tannin (at 30 or 130 μg/ml) activated an inositol phospholipase C in alveolar membranes. Phosphatidylcholine phospholipases C and D were found only at the higher concentration of tannin.