a) Respiratory bronchiolitis: the intra-alveolar accumulation of finely pigmented macrophages (smoker’s macrophages) (haematoxylin and eosin, 400×). a) Respiratory bronchiolitis: the intra-alveolar accumulation of finely pigmented macrophages (smoker’s macrophages) (haematoxylin and eosin, 400×). Generally smoker's macrophages have a strict bronchiolocentric distribution (b; haematoxylin and eosin 40×), but occasionally they involve the entire lobule (c; haematoxylin and eosin, 20×). d) Respiratory bronchiolitis in a 63-yr-old heavy smoker who was asymptomatic at the time of computed tomography. The high-resolution computed tomography image shows bilateral poorly defined centrilobular nodules in the upper lobes. e) Occasionally, particularly in desquamative interstitial pneumonia, a relatively large number of eosinophils are present and the limits with chronic eosinophilic pneumonia are sometimes blurred (haematoxylin and eosin, 200×). Antonella Caminati et al. Eur Respir Rev 2012;21:207-217 ©2012 by European Respiratory Society