In addition it has been shown that during the course of pulmonary fibrosis the increase of TGF-β1 mRNA precede the increase of type I and type III procollagen mRNAs The secretion of biologically active TGF-β1 by alveolar macrophages is transiently elevated in bleomycin -induced pulmonary inflammation, whereas latent (L)-TGF-β1 secretion remains elevated for a prolonged length of time and it is probable that the extent of inflammation and fibrosis in this model depends on the quantity of active TGF-β1 available [70]. This evidence concerns the gene TGFB1 and pulmonary fibrosis.