Transforming growth factor-beta and its role in asthma.

Transforming growth factor-beta (TGF-beta) is an important fibrogenic and immunomodulatory factor that may play a role in the structural changes observed in the asthmatic airways. In vitro as well as in vivo studies have evidenced a dual role for TGF-beta: it can either function as a pro- or anti-inflammatory cytokine on inflammatory cells, participating into the initiation and resultion of inflammatory and immune responses in the airways. TGF-beta is also involved in the remodelling of the airway wall, and has in particular been related to the subepithelial fibrosis. TGF-beta is produced in the airways by inflammatory cells infiltrated in the bronchial mucosa, as well as by structural cells of the airway wall including fibroblasts, epithelial, endothelial and smooth muscle cells. By releasing TGF-beta, these different cell types may then participate into the increased levels of TGF-beta observed in bronchoalveolar lavage fluid from asthmatic patients. Taken together, these results suggest that TGF-beta may play a role in inflammation in asthma. However, as its role is dual in the modulation of inflammation, further studies are needed to elucidate the precise role of TGF-beta in the airways.