Airway mucosal inflammation in COPD is similar in smokers and ex-smokers: a pooled analysis. by Gamble, E, Grootendorst, D, Hattotuwa, K, O'Shaughnessy, T, Ram, F, Qiu, Y, Zhu, J, Vignola, A, Kroegel, C, Morell, F, Pavord, I, Rabe, K, Jeffery, P, Barnes, N