Loss of IDO was not protective (Figure 7D and Supplemental Figure 8); however, inhibition of TDO2 significantly decreased both collagen mRNA expression and deposition and expression of the myofibroblast marker α–smooth muscle actin (α-SMA) during blm-induced pulmonary fibrosis, as well as fibrotic pathology, as assessed by trichrome staining of lung sections (Figure 7, E–H). This evidence concerns the gene ACTA1 and pulmonary fibrosis.