TGF-β1 induces the expression of collagens type I and type III. A549 cells were incubated with 5 ng/ml of TGF-β1 in the presence of 5 μg/ml of L-ascorbic acid for 72 h. (A) mRNA expression of collagens type I and type III was detected using RT-PCR. Densitometric analysis was performed. The changes of expression level are expressed as fold increase compared to the control. Each bar represents the mean ± SD of three independent experiments. ** P < 0.01. (B) Protein expression of collagens type I and type III was detected by immunocytochemical staining. Panels (a) and (b) represent collagen type I and panels (c) and (d) represent collagen type III expression, respectively. TGF-β1 induces collagen type I and type III expression in A549 as shown in panel (b) and (d).