Time course of collagen type I (a) and HSP47 (c) mRNA expression in A549 cells incubated with 5 ng/ml of TGF-β1 analyzed by Northern blotting. Collagen type I (b) and HSP47 (d) mRNA expression was significantly increased in A549 cells after 6 and 48 h incubation with 5 and 10 ng/ml of TGF-β1, respectively. Density of mRNA and GAPDH bands was compared and results are shown as ratios. Values are means ± SEM of four experiments. *P < 0.05, compared with control.