Primary AT2 cells were obtained as previously described (45 (link)). In brief, lungs were lavaged three times with phosphate-buffered saline (PBS) containing 1% antibiotics, then digested with dispase II (2 mg/ml) and deoxyribonuclease I (0.3 U/ml) at 37°C for 45 min, and minced. The digested lung pieces were filtered through 100- and 40-μm cell strainers and centrifuged. Cell pellet was resuspended with DMEM containing 10% FBS and cultured at 37°C for 45 min in CD16/32- and CD45-coated dishes to remove inflammatory cells. The supernatant was further cultured at 37°C for 45 min to remove fibroblasts. Then, cells were resuspended with DMEM/F12 containing 10% FBS, seeded in collagen I (BD)–precoated plates, and cultured at 37°C with 5% CO2. AT2 cells were characterized by immunofluorescence staining using antibody against Prospc (Santa Cruz Biotechnology).