Parathyroid hormone related protein is localized in the granular layer of normal skin and in the dermal infiltrates of mycosis fungoides but is absent in psoriatic lesions.

Biopsies of normal and diseased skin were immunohistochemically investigated for the presence of parathyroid hormone-related protein (PTH-rp). In normal skin and several skin disorders a monoclonal antibody against the 34-68 sequence of PTH-rp was found to be exclusively located in the granular layer. PTH-rp could not be detected in untreated psoriatic plaque lesions even when a granular layer was present. Psoriatic lesions improving after 1-2 weeks' treatment with betamethasone or vitamin D3 analogue revealed PTH-rp reactivity just above the granular layer. These findings substantiate a possible role for PTH-rp as a growth inhibitor. In the dermis the granular layer in the upper part of the hair follicles was stained for PTH-rp and the dermal infiltrates in 5 of 10 patients were stained with mycosis fungoides.