Our quantification of lung fibrosis revealed that the 2 groups with WT PAI-1 expression (DTR+:WT and DTR+:VTN–/–) developed statistically significantly increased lung collagen content in response to DT (relative to the negative control group), while the 2 groups deficient in PAI-1 expression (DTR+:PAI-1–/– and DTR+:PAI-1–/–:VTN–/–) were protected (Figure 1C). The gene discussed is SERPINE1; the disease is pulmonary fibrosis.