SMAD2 and pulmonary fibrosis: Immunostaining showed phosphorylated SMAD2/3 in GFP+, Krt8+ AT2-lineage cells and αSMA+ myofibroblasts (triangles in Fig. 7a and Supplementary Fig. 6a), suggesting that the canonical TGF-β-SMAD pathway is activated in AT2-lineage cells in BLM-induced lung fibrosis.