PDGFRB and pulmonary fibrosis: Moreover, 4 weeks after bleomycin treatment, there was a marked increase in lung fibrosis in Ctnnb1-knockout mice, as assessed by anti-PDGFRa, anti-PDGFRb, anti-collagen I, and anti-collagen IV immunofluorescence staining and Sirius red staining of lung sections (Fig. 7i–l).