KRT5 and idiopathic pulmonary fibrosis: In lungs with idiopathic pulmonary fibrosis (IPF), decreased AT2 stemness is associated with diminution of AT1 and AT2-AT1 transitional state cells and the appearance of an aberrant epithelial cell population characterized by the expression of airway epithelial marker keratin 17 (KRT17), but negative for the basal cell marker KRT5.