Previous studies reported that CD26/DPP4 expression is locally regulated in fibrotic tissues and CD26/DPP4 is a marker of activated skin fibroblasts (Soare et al., 2020), while its expression may not be associated with an activated fibroblast phenotype in human lung fibroblasts from IPF patients (Kadefors et al., 2022). This evidence concerns the gene DPP4 and idiopathic pulmonary fibrosis.