Glucocorticoid inhibition of RANTES expression in human lung epithelial cells

An influx of eosinophils into the lungs occurs in several pulmonary disorders. However, the mechanisms involved remain unknown. Lung epithelial cell release of eosinophil chemotactic factors such as RANTES or macrophage inflammatory protein-1 alpha (MIP-1 alpha) could account for the influx of eosinophils into the lungs. In order to demonstrate the potential role for lung epithelial cells to release RANTES and/or MIP-1 alpha, we investigated the mRNA expression and protein release in cultured A549 cells. Tumor necrosis factor-alpha (TNF alpha) and interleukin-1 beta (IL-1 beta) induced a time- and dose-dependent increase in RANTES mRNA expression and protein release. In contrast, MIP-alpha protein release was not detectable in these cells. As corticosteroids decrease the influx of eosinophils into the lungs in vivo, we also investigated the capacity of dexamethasone to decrease the TNF alpha-induced RANTES release and mRNA expression; both were decreased in a time- and concentration-dependent manner. Dexamethasone did not affect the TNF alpha-induced RANTES mRNA half-life and did not require protein synthesis to manifest an inhibitory effect. Supernatant from cells stimulated with TNF alpha and IL-1 beta increased eosinophil chemotaxis and this was also inhibited by dexamethasone. These findings suggest a role for RANTES release by lung epithelial cells in the recruitment of eosinophils into the lungs in pulmonary disorders such as interstitial lung diseases, idiopathic pulmonary fibrosis, or asthma and suggest that one beneficial effect of corticosteroids may be inhibition of lung epithelial cell RANTES mRNA expression and protein release.