Fig. 1.

Asbestos exposure-induced generation of fibrogenic alveolar macrophages with high production of TGF-β. The illustration shows the more significant contribution of alveolar macrophages (AM) to asbestos-caused lung fibrosis by production of TGF-β, in addition to production of inflammatory cytokines. TNF-α produced by AM early after exposure to asbestos stimulates fibroblasts or lung epithelial cells to produce TGF-β, leading to production of extracellular matrix (ECM) (left). However, as demonstrated by our studies, asbestos exposure induces generation of fibrogenic AM with high production of TGF-β and enhanced survival. It is probable that these AM contribute to accumulated production of ECM by their long-lasting production of TGF-β in addition to an inflammatory response (right)