Higher percentages of type II pneumocytes [24,27,71], endothelial cells [71,72,73], and pulmonary artery smooth muscle cells [74] with positive staining for p16 or p21 were observed in lung tissue sections from patients with COPD or emphysema compared to smokers [27,71,72,73] or non-smoking controls [27,71]. Here, CDKN2A is linked to chronic obstructive pulmonary disease.