alpha-Defensins, antimicrobial peptides produced mainly by neutrophils, have been reported to be associated with a wide variety of lung diseases, including idiopathic pulmonary fibrosis (IPF), cystic fibrosis (CF), and diffuse panbronchiolitis (DPB). In each disease, alpha-defensins are located in different areas, such as around the alveolar septa in IPF and around the airways in CF and DPB, suggesting that alpha-defensins play different roles. Meanwhile, growth factors are known to contribute to IPF, CF, and DPB. alpha-Defensins are known to induce interleukin (IL)-8 in airway epithelial cells, but the effects of alpha-defensins on the release of growth factors from various components in the lung have not been sufficiently investigated. In the present study, the in vitro effects of human neutrophil peptide (HNP)-1 (a subtype of alpha-defensin) on the expressions of IL-8 and growth factors in lung fibroblasts, bronchial epithelial cells, and alveolar epithelial cells were examined. HNP-1 mainly enhanced the expression of IL-8 in epithelial cells, whereas it enhanced transforming growth factor-beta and vascular endothelial growth factor expressions in lung fibroblasts. These results suggest that alpha-defensins play different roles in the pathogenesis of IPF, CF, and DPB according to the location in the lung where the alpha-defensins are mainly produced.