Increased airway epithelial and T-cell apoptosis in COPD remains despite smoking cessation

Abstract

There is heterogeneity in the propensity of smokers to develop chronic obstructive pulmonary disease (COPD), and improved treatment strategies are hindered by limited understanding of COPD pathogenesis, especially as distinct from the effects of smoking per se. Although apoptosis is essential for tissue homeostasis, increased apoptosis may cause tissue damage and inflammation. This study addressed whether airway T-lymphocytes and airway epithelial cells (AEC) show an increased likelihood of undergoing apoptosis in COPD and if this was related to smoking. Apoptosis (7-amino-actinomycin D, Annexin, single-stranded DNA and caspase), Bcl-2, Bax and p53 were assessed in cells obtained from bronchial bushing and bronchoalveolar lavage from ex- and continuing smokers with COPD, and nonsmoking controls, using flow cytometry. A mean 87% increase in apoptosis of AEC and a 103% increase in T-lymphocyte apoptosis were found in COPD. There were no significant differences in apoptosis of AEC between current and ex-smokers with COPD. Apoptosis may contribute to chronic obstructive pulmonary disease pathogenesis, and continued excess apoptosis after smoking cessation may offer a new target for therapeutic interventions. Whether the persistence of increased apoptosis after smoking cessation results from changes in the pulmonary milleau after years of noxious insult, or whether some individuals have a natural predisposition toward increased apoptosis and possible development of chronic obstructive pulmonary disease remains to be determined.