TDO2 and idiopathic pulmonary fibrosis: Further in contrast to this study, we found that genetic deletion of IDO1 had no effect on fibrogenesis or expression of IL-6 (Figure 7D and Supplemental Figure 8), and we found no evidence of IDO expression in analysis of fibroblast subsets from patients with IPF (Supplemental Figure 7B), while treatment of mice and fibrotic fibroblasts with the specific TDO2 inhibitor 680C91 decreased kynurenine production, ameliorated fibrosis, and reduced collagen production and expression of the myofibroblast marker α-SMA (Figure 7).