Coincidence of PAS-stained areas and CLCA1-expressing cells in airway epithelium. Lung sections were stained with PAS (A-C) or immunohistochemically stained with anti-CLCA1 antibody (D-F). (A, D) Airway epithelium of a non-smoker. Few mucus and CLCA1-expressing cells were detected. (B, E) Airway epithelium of a smoker without COPD. Increased numbers of mucus secretory cells, mostly goblet cells, were observed. (C, F) Airway epithelium of a COPD patient. Significant coincidence between mucus overproduction and CLCA1 expression was observed. Scale bars = 50 μm.