Cell culture

Human bronchial epithelial cells (cell line BEAS-2B) were used in this study (CRL-9609; American Type Culture Collection, Rockville, MD, USA). BEAS-2B cells were cultured in RPMI-1640 medium (Invitrogen, Carlsbad, CA, USA) with 10% fetal bovine serum and maintained at 37 °C in a humidified atmosphere of 5% carbon dioxide and 95% air. The cells were maintained at 37 °C, between 30 and 90% confluence, in an air-ventilated and humidified incubator maintained with 5% carbon dioxide. For subculturing, the cells were trypsin-dissociated and passaged every 2–4 days.