Abstract
Even if a lot of the “hows” for AHR in COPD are known, the “whys” have still not been answered. It is not known if AHR truly denotes a susceptibility to smoking, in line with the Dutch hypothesis, or if it is a mere reflection of the progression in COPD. AHR is, unlike in the case of asthma, resistant to current treatments, and extremely little is known of the underlying airway biology associated with AHR in COPD.