Lung Cytokine Production in Bleomycin-induced Pulmonary Fibrosis

In bleomycin-induced pulmonary fibrosis, lung injury is accompanied with inflammation and subsequent fibrosis. In this study, lung mRNA for several cytokines was measured in bleomycin-treated mice to evaluate their roles in lung fibrosis. Significant increases in tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) mRNA were found in lungs of bleomycin-treated responder CBA mice but not in nonresponder BALB/c mice. Increases in responder animals peaked on day 7 after bleomycin administration, and subsequently returned toward control levels. This time course paralleled that for the increase in beta-actin mRNA, but preceded the peak increase in mRNA for collagens I and III. When lung macrophages were analyzed for cytokine secretion, differences were observed between alveolar macrophages and interstitial cells, and between cells from bleomycin-responsive CBA and nonresponsive BALB/c mice. Only alveolar macrophages from CBA mice secreted increased amounts of IL-1. TNF-alpha activity was increased in conditioned media of alveolar and interstitial cells of CBA mice, while only alveolar macrophages of nonresponder BALB/c mice secreted any activity. The kinetics of the increased secretion of TNF-alpha was dissimilar for these different cells. These results are consistent with the conclusion that increased production of TNF-alpha and TGF-beta is an important component of the fibrotic process.