Whilst we did not demonstrate any basal differences in antioxidant enzyme activities between the ex-smoking COPD and the healthy never smoking control groups, it is likely that such a functional impairment in Nrf2 signalling is only manifest when the airway is stressed, such as would occur as a result of cigarette smoke inhalation, or during exacerbations. Here, NFE2L2 is linked to chronic obstructive pulmonary disease.