The distal airway epithelium of COPD patients was found to contain significantly higher percentages of CC10-positive cells that were positive for p16, CC10-positive cells that were positive for phospho-p38 MAPK, and CC10-positive cells that were positive for both p16 and phospho-p38 MAPK than the distal airway epithelium of asymptomatic nonsmokers (Figure 9A and 9B). This evidence concerns the gene CDKN2A and chronic obstructive pulmonary disease.