MUC5B and idiopathic pulmonary fibrosis: Viewed in this context, the DNase and MNase accessibility at the MUC5B enhancer in non–MUC5B-expressing cells types (e.g., in vitro data for embryonic stem cells, cardiac cell types, and BEAS-2B cells and in vivo data for vascular endothelial cells) is relevant to IPF-associated MUC5B expression in terminal bronchiolar-like regions, which do not normally express MUC5B (43).