PARATHYROID-HORMONE-RELATED PROTEIN IN SARCOIDOSIS

Parathyroid-hormone-related protein (PTHrP) is the main mediator of th e humoral hypercalcemia of malignancy. It is also detected in many nor mal adult and fetal tissues. Altered calcium metabolism occurs in sarc oidosis, and two cases of sarcoidosis with hypercalcemia and elevated plasma PTHrP are described. An archival study of 20 lymph node biopsie s with the pathological diagnosis of sarcoidosis was performed. Immuno histochemistry using a polyclonal antiserum to human PTHrP and in situ hybridization using a riboprobe to human PTHrP were performed on the lymph node biopsies. Immunohistochemistry for PTHrP was also performed on the biopsies from the two cases with elevated plasma levels. Immun ohistochemical analysis detected PTHrP in macrophages within granuloma ta in 17 of the 20 (85%) biopsies. In situ hybridization detected a po sitive signal for messenger RNA in the granulomata of 11 of 19 (58%) b iopsies. PTHrP immunoreactivity and PTHrP gene expression are present in sarcoid granulomata. PTHrP may contribute to the hypercalcemia of s arcoidosis.