MUC5B and idiopathic pulmonary fibrosis: Pathologically, IPF is characterized by bronchiolization of distal airspaces, whereby fibrotic “honeycomb” cysts are frequently lined by airway-type mucociliary epithelium—including p63+/KRT5+ basal cells, ciliated cells, and MUC5B-producing goblet cells—rather than by normal alveolar epithelium [39].