NHBE or SAE cell culture. Primary normal human bronchial epithelial (NHBE) or small airway (SAE) cells were obtained from Lonza. Te cells were cultured in a T75 fask for 2–4 days until they reached 80% confuence.The cells were trypsinised and seeded onto collagen (Corning collagen I, Rat tail)-coated 0.33 cm2 porous (0.4µm) polyester membrane inserts with a seeding density of 1×105 cells per Transwell (Costar, Corning). Te cells were grown to near confuence in submerged culture for 2–3 days in specifc epithelial cell growth medium according to the manufacturer´s instructions. Cultures were maintained in a humidifed atmosphere with 5% CO2 at 37 °C and then transferred to ALI culture. Te epithelium was fed with B-ALI or S-ALI diferentiation medium (Lonza). The number of days in development was designated relative to initiation of ALI culture, corresponding to day 0. Cells were used between day 50 to day 70 in ALI and under perfusion.
TEER values were measured using EVOM voltohmmeter with STX-2 chopstick electrodes (World Precision Instruments, Stevenage, UK). Measurements on cells in ALI culture were taken immediately before the medium was exchanged. For measurements, 0.5ml and 1.0ml of medium were added to the apical and basolateral chambers, respectively. Cells were allowed to equilibrate before TEER was measured. TEER values reported were corrected for the resistance and surface area of the Transwell flters.