These findings highlight the importance of AP-3 in mediating LB maturation in AT2 cells and suggest that mutated AP-3 may contribute to the pathogenesis of HPS2/10-associated pulmonary fibrosis by altering alveolar epithelial cell homeostasis upon impairing the transport of key cargoes to LBs. This evidence concerns the gene AP3B1 and pulmonary fibrosis.