KRT5 and chronic obstructive pulmonary disease: Milara et al. reported that primary AECs isolated from smokers or COPD patients expressed higher levels of mesenchymal markers (alpha smooth muscle actin, vimentin and type 1 collagen) and lower levels of epithelial markers (E-cadherin, Zo1 and cytokeratin 5/18) than those from non-smokers [8].