The mesenchyme marker platelet-derived growth factor receptor (PDGFR)-β is expressed by many of these mesenchymal cell types, including fibroblasts, pericytes, Gli1+ mesenchymal stem cell (MSC)-like cells and Axin2+ progenitors14,15,18, but no prior studies have utilized cell labeling driven by an inducible Pdgfrb promoter for fate mapping in lung fibrosis. This evidence concerns the gene PDGFRB and pulmonary fibrosis.