CLDN10 and idiopathic pulmonary fibrosis: Most importantly, our results indicate that the transition of club cells from CCSP- and Cldn10-positive to a solely Cldn10-positive state in IPF bronchioles, is spatially associated with fibroblastic foci even though it still remains to be elucidated whether such pheno-conversion of club cells is a cause or a result of myofibroblastic phenoconversion of the underlying fibroblasts.