DPP4 and pulmonary fibrosis: In our bleomycin-induced pulmonary fibrosis study, the numbers of fibroblasts and myofibroblasts in Dpp4 KO mouse lungs after bleomycin treatment were lower than those in wild-type (WT) mice, and the suppression of CD26/DPP4 expression by the small interfering RNA (siRNA) treatment had inhibitory effects on lung fibroblasts’ activation in vitro [24].