Tight junctions form a barrier in human epidermis.

Tight junctions (TJ) are cell-cell junctions that have proved to form a paracellular barrier for solutes and water between cells of epithelia, including the stratum granulosum of the stratified epithelium of the epidermis of newborn mice. In mice lacking claudin-1, a major barrier-forming TJ component, this barrier was abolished. However, the role of TJ in human skin is controversially discussed as unambiguous data were missing so far. Here, we investigated TJ barrier function in healthy human skin as well as in skin samples from psoriatic lesions which are characterized by an altered localization of TJ proteins. We demonstrate for human skin that occludin- and claudin-1-positive sites in the stratum granulosum form a barrier for extracellular biotin-SH (557Da) and that in psoriatic skin the localization of the barrier and the TJ proteins are altered in parallel.