(A) Epithelial inflammation, driven by exogenous TNF-α, IL-1β, and IL-6, induces barrier dysfunction, witnessed by a dramatic decrease in TEER in each group (NS, Smo, COPD 1–2, COPD3-4). (B, C) Cytokine-induced epithelial inflammation induces EMT in Smo and COPD-derived ALI AE, witnessed by increased fibronectin release in early, short-term, and mid-term cultures (B) and vimentin expression in mid-term cultures (C). (B, C) The absolute increase in fibronectin (B) and vimentin (C) was significantly higher in mid-term COPD AE than in non-COPD AE (pooled Smo and NS, labeled “no COPD”). (D) Cytokine-induced epithelial inflammation deteriorates the epithelial polarity, witnessed by the SC apical release. No difference was seen in (very) severe COPD because of low baseline levels. *, **, **** indicate P-values of less than 0.05, 0.01, and 0.0001. Bars indicate median ± interquartile range (B, C, D) and mean ± SEM (A, E). AE, airway epithelium; ALI, air-liquid interface; COPD, chronic obstructive pulmonary disease; CT, controls; EMT, epithelial-to-mesenchymal transition; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; IL, interleukin; NS, non-smokers; ns, not significant; SC, secretory component; SEM, standard error of the mean; Smo, smokers; TEER, transepithelial electric resistance; TNF-α, tumor necrosis factor α; w, weeks.