In order to investigate putative differences in airway epithelial cell differentiation between COPD and control, PBECs from COPD and control subjects (Table 1, COPD patients 6–16 and control subjects 7–17) were differentiated at ALI culture in the absence of IL-13, and gene expression and DNA methylation levels were compared in the total cell population after 14 days of ALI culture (Fig. 4a). The gene discussed is IL13; the disease is chronic obstructive pulmonary disease.