Furthermore, some members of the claudin protein family, which are known to interact with ZO-1, and thereby contributing to the TJ organisation [115], were shown to be differentially expressed in CF vs. non-CF human bronchial epithelial cells: claudin-1 and 4 being expressed in non-CF cells and only claudin-1 being expressed in CF cells, while claudin-4 expression was lost during polarization [110]. Here, CLDN4 is linked to cystic fibrosis.