The pan-cytokeratin level normalized to β-actin was increased in 18W-Sm mice but decreased in 30W-Ex (Figure 4B), reconfirming that the lung histology of 30W-Ex mice, not 18W-Sm mice, was similar to human emphysema, where lung epithelial cells are decreased in number. The gene discussed is ACTB; the disease is pulmonary emphysema.