ABCG2 and asthma: It is clear that ABC transporters are i) variably expressed in epithelial cells from different airway generations, ii) regulated by cigarette smoke exposure, and iii) differentially expressed in individuals with COPD and asthma, We further demonstrate that an in vitro cell culture system is amenable to investigate the consequences of differential expression patterns of candidate ABC transporters, creating a foundation for further mechanistic research into the basic biology of ABC transporters in lung health and disease.