KRT5 and idiopathic pulmonary fibrosis: Next, we stained serial lung tissue sections of organ donor and IPF patients’ lungs with cytokeratin 5 (KRT5, a marker for airway basal cells), proSP-C, HOPX, and cytokeratin 7 (KRT7, a marker for general epithelia), and Ki67, to show the expression pattern of HOPX and proSP-C as well as their proliferation status in IPF lungs (Fig. 4G and H).