COPD airways have increased mucous expression and epithelial cell count. Representative image of human lung tissues from (A) non-COPD, (B) COPD GOLD STAGE 2, and (C) COPD GOLD STAGE 4 stained with periodic acidic Schiff (PAS) for total carbohydrate content on mucous expression in the airway epithelium were shown. (D) Airway epithelial-specific PAS+ cells were normalized to the length of basement membrane in subjects without COPD, COPD GOLD STAGE 2 and GOLD STAGE 3/4. Correlations between airway epithelial-specific PAS+ cells with (E) FEV1/FVC (%) and (F) total epithelial cell count were shown. The Kruskal–Wallis test with Dunnett’s multiple comparisons test was used in panel D. Linear regression analyses were used in panels E and F. Red dot = non-COPD, blue dot = COPD GOLD STAGE 2, orange dot = COLD GOLD STAGE 3/4. (Note: one non-COPD subject has missing FEV1/FVC value).