We found that epithelial cells derived from patients with COPD had significantly higher mRNA expressions of MUC5AC, AGR2, and SPDEF than epithelial cells from controls (MUC5AC, 21.1-fold; SPDEF, 1.9-fold; AGR2, 2.9-fold, Fig. 4b), whereas no difference was found in FOXA2 and FOXJ1 expression between COPD-derived cells and control-derived cells (Fig. 4b and Additional file 7: Figure S6). Here, SPDEF is linked to chronic obstructive pulmonary disease.