DPP4 and pulmonary fibrosis: In this study, we aimed to clarify the functional roles of CD26/DPP4 in pulmonary fibrosis by focusing on fibroblast activation and EndMT using Dpp4‐deficient mice in the model of BLM‐induced pulmonary fibrosis (Liu et al., 2017), and in cultured human lung fibroblasts (HLFs).