Cell culture
All materials were purchased from Sigma (St Louis, Missouri, USA) unless otherwise stated. The alveolar type II-like cell line A549 was cultured in Dulbecco Modified Eagle Medium (DMEM) supplemented with 10% (v/v) heat-inactivated FBS, 2 mM L-glutamine and 100 U/mL penicillin/streptomycin. The bronchial epithelial cell line BEAS-2B was cultured in bronchial epithelial growth media (BEGM; Lonza) supplemented with BEGM bullet kit (Lonza) and grown on tissue culture plastic coated with 0.01 mg/mL fibronectin, 0.03 mg/mL collagen and 0.01 mg/mL bovine serum albumin (BSA). Cells were cultured in a humid atmosphere at 37 °C, 5% (v/v) COThe day before exposure, A549 cells were seeded at a density of 1.2 × 10