Parathyroid hormone-related peptide: immunolocalisation in normal salivary glands and in pleomorphic adenomas

Parathyroid hormone-related peptide (PTHrP) has been shown to be produced as an early step in the differentiation sequence and is considered to be a marker of some progenitor cells. We investigated the presence and distribution of PTHrP in 7 normal parotid glands and in 18 salivary pleomorphic adenomas (PA). Localisation of PTHrP was studied by immunohistochemistry with a three-step unlabelled peroxidase-antiperoxidase method. In the normal glands PTHrP is found mainly in the basal and dark cells, and to a lesser extent in the light cells of the ducts. In PA the inner layer of tubulo-ductal structures and all cells of the cyst-like structures show strong positivity for PTHrP. Scattered cells in the dense clusters also stain strongly. Virtually all tumour cells in myxoid and chondroid areas are devoid of staining. In clusters of squamous metaplasia, most cells are slightly positive and scattered cells are stained strongly. PTHrP contributes to cellular differentiation and is also related to keratinisation. We suggest that the PTHrP-positive inner layer cells in pleomorphic adenomas represent a step in the squamous differentiation and in the further elaboration of the tubulo-ductal structures.