PTN stimulates fAEC II proliferation. Primary fAEC II were cultured in serum-free medium on plastic dishes. The cells were treated with 50 ng/ml PTN at day 1. After 36 h, the cells were collected and stained with anti-BrdUrd (BrdU) antibodies to view the proliferating cells. A, representative images. BF, brightfield. B, quantitation. The proliferating cells (BrdUrd-positive cells) were expressed as a percentage of total cells (means ± S.E.). *, p < 0.05 versus control, n = 5.