To explain the mucin-expressing structures in IPF pathogenesis, Seibold et al. analyzed ciliated, basal, and alveolar type II cells in lung tissue and reported predominant expression of MUC5B in pseudostratified mucociliary epithelium comprised of basal epithelial cells and mucus cells in distal airway. Here, MUC5AC is linked to idiopathic pulmonary fibrosis.