TGFβ1 overexpression induces pronounced fibrotic response following bleomycin exposure. Tissue fibrosis was assessed in both Tr- wild type (A) and Tr+ transgenic (B) mice lung following exposure to 4500 IU bleomycin, as previously described. Shown are representative micrographs following haematoxylin/eosin staining of lung tissue, demonstrating fibrotic response in bleomycin treated wild type mouse lung that is significantly more severe in tissue from Tr+ TGFβ1 transgenic mice, suggesting that overexpression of the TGFβ1 transgene exacerbates subsequent lung injury. C. To quantify this fibrotic effect, fibrosis scores were determined as described. The graph shows enhanced fibrosis scores in Tr+ TGFβ1 transgenic mice versus their Tr- wild type counterparts in response to bleomycin exposure.