As expected, DUOX1 protein was prominently expressed in the bronchial and small airway epithelium, and small airway DUOX1 expression was found to be reduced in tissue sections from patients with COPD, especially in patients with very severe COPD (GOLD IV), compared with age-matched, non-COPD controls (Figure 1, A and B, with representative images of a scoring scale 1–4; Supplemental Figure 1). This evidence concerns the gene DUOX1 and chronic obstructive pulmonary disease.