Upregulation of PD−L1 in the lungs of IPF patients and mice with pulmonary fibrosis induced by bleomycin and TGF−β were detected. Fibroblast PD−L1 may promote pulmonary fibrosis through both Smad3 and β−catenin signaling. This evidence concerns the gene TGFB1 and idiopathic pulmonary fibrosis.