In clustered, cystic airspaces termed honeycomb cysts in IPF, this transitional state is marked by expression of one or more keratin genes (KRT5 and KRT14) and in simple cysts, by KRT8 and KRT18 in the bleomycin mouse model (11, 56, 57). This evidence concerns the gene KRT5 and idiopathic pulmonary fibrosis.