In regard to the ontology of the MUC5B+ club cells migrating to the alveoli in IPF, our previous study demonstrated that MUC5B is highly expressed in normal human small airway club cells [3], i.e., SCGB1A1+ MUC5B+ club cells in broncholarization of the IPF lung might be the result of migration of club cells from human small airway epithelium [20, 36]. The gene discussed is MUC5B; the disease is idiopathic pulmonary fibrosis.