At Boston University Medical Center, healthy volunteer never smokers (n = 6) and current smokers (n = 6) underwent a bronchoscopy to obtain brushings from the right mainstem bronchus, as described previously (17, 18). Eligible volunteers included subjects who (i) were between the ages of 19 and 55; (ii) did not use inhaled or intranasal medications; (iii) did not have a history of chronic obstructive pulmonary disease, asthma, pulmonary fibrosis, sarcoid, or head and neck/lung cancer; (iv) did not use marijuana; (v) did not have a respiratory infection within the past 6 weeks; and (vi) did not use other tobacco products (i.e., pipe, cigar, and chewing). Spirometry was performed to assess lung function (e.g., FEV1/FVC). Exhaled carbon monoxide (Smokerlyzer Carbon Monoxide Monitor, model EC-50; Bedfont Scientific Ltd.) and urine cotinine (NicAlert; Confirm BioSciences) levels were measured to confirm smoking status. The Institutional Review Board approved the study, and all subjects provided written informed consent.