Moreover, MUC5B overexpression and mislocalization to terminal airways and honeycomb cysts are commonly observed in IPF and are associated with the MUC5B promoter variant (9, 10), and transgenic Muc5b mice have been shown to be more susceptible to the fibroproliferative effects of bleomycin (11). Here, MUC5B is linked to idiopathic pulmonary fibrosis.