BACKGROUND: Subepithelial fibrosis plays a major role in the development of irreversible airway obstruction in asthma. Eosinophils are major effector cells in allergic inflammation, and it has been suggested that eosinophil-derived mediators such as transforming growth factor-beta (TGF-beta) play a role in the pathogenesis of airway remodeling. OBJECTIVE: The aim of this study was to evaluate whether eosinophils activated by IL-5 plays a major role in the collagen gel contraction by lung fibroblasts. METHOD: Various cell numbers of lung fibroblasts were cultured in collagen gels to determine the appropriate numbers of fibroblasts. Purified human peripheral blood eosinophils were activated by IL-5 for 3 days, and TGF-beta mRNA expression was evaluated using semiquantitative RT- PCR. The cultured supernatants with or without TGF-beta were added to the collagen gel media with lung fibroblasts, and collagen gel diameter was serially measured to evaluate collagen gel contraction. RESULTS: The amount of collagen gel contraction was significantly associated with the number of fibroblasts (p< 0.05), and TGF-beta significantly contracted the collagen gel to contract in a dose-dependent manner (p< 0.05). However, supernatants derived from IL-5-activated eosinophils did not contract the collagen gel compared to controls (p> 0.05). Moreover, expression of TGF-beta mRNA in eosinophils was the same before and after stimulus of IL-5. CONCLUSION: Activated eosinophils by IL-5 may play a minor role in the collagen gel contraction by lung fibroblasts.