Pulmonary fibrosis can complicate diverse pulmonary and systemic pathologies. In many cases the underlying cause remains unidentified. Mortality from the disease is increasing steadily in the UK and USA. The clinical features are well-described, but patients frequently present at an advanced stage, and current treatments have not improved the poor prognosis. There is a compelling need to identify the fibrotic process earlier and to develop new therapeutic agents. Increased collagen deposition is central to the pathology and interest over the last decade has focused on the role of cytokines in this process. These polypeptide mediators are believed to be released from both circulating inflammatory and resident lung cells in response to endothelial and epithelial injury. Key cytokines currently implicated in the fibrotic process are transforming growth factor-beta, tumour necrosis factor-alpha and endothelin-1. This article outlines the evidence implicating these mediators in the pathogenesis of pulmonary fibrosis and also considers the possible role of cytokines with antifibrotic effects, such as interferon-gamma. The "balance" of positively and negatively regulating cytokines is discussed, and the potential for interaction with other factors including viruses, hormones and altered antioxidant status is also considered. Finally, potential novel therapeutic approaches are discussed, together with suggestions for future studies and clinical trials. As the outcomes of different avenues of research over the last ten years are brought together, it is clear that there is now a hitherto unrivalled opportunity to begin to tackle the treatment of this devastating disease.

D Di iv ve er rs se e c ce el ll lu ul la ar r T TG GF F--β 1 1 a an nd d T TG GF F--β 3 3 g ge en ne e e ex xp pr re es ss si io on n i in n n no or rm ma al l h hu um ma an n a an nd d m mu ur ri in ne e l lu un ng g This procedure was technically simple, providing excellent resolution. TGF-β 1 and TGF-β 3 messenger ribonucleic acid (mRNA) transcripts were detected in a wide variety of cells. In human lung, mRNA for both isoforms was localized to bronchiolar epithelium and alveolar macrophages. TGF-β 1 , but not TGF-β 3 mRNA was detected in mesenchymal and endothelial cells. In murine tissue, TGF-β 1 , mRNA was localized to bronchiolar epithelium, Clara cells, mesenchymal cells, pulmonary endothelium and alveolar cells, including macrophages. TGF-β 3 mRNA was similarly distributed but not detected in endothelium.In summary, using a nonisotopic technique in lung tissue, we have detailed the cells expressing the transforming growth factor-β 1 and β 3 genes in human and murine lung. There was widespread expression of these cytokines in normal lung consistent with autocrine or paracrine roles in regulating cellular turnover, immune defence and matrix protein metabolism.

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