PCNA Cell proliferation immunostaining of cultured embryonic lungs. (A-C) Embryonic lungs treated with tammar milk and (D) control. Cell proliferation in both mesenchyme and epithelium was detected by immunostaining with PCNA antibody and counterstained with haematoxylin. (E-H) Higher magnification views of A-D. (A,E) Embryonic lung treated with day 20 milk showed low cell proliferation in both epithelium and mesenchyma. (B,F) Embryonic lung treated with day 60 milk showed cell proliferation in both epithelium and mesenchyma around the terminal end buds. (C,G) Embryonic lung treated with day 120 milk showed cell proliferation in both mesenchyma and epithelium. The distribution of mesenchyma was increased in explants treated with day 60 (B,F) and 120 (C,G) milk when compared to explants treated with day 20 (A,E) milk. (D,H) Lung cultured in control media showed a low level of cell proliferation. Scale bar 100 μm.