Detection of melanocortin-1 receptor antigenicity on human skin cells in culture and in situ

The proopiomelanocortin (POMC) products alpha-melanocyte stimulating hormon e (alpha-MSH) and adrenocorticotropin (ACTH) bind to specific receptors kno wn as the melanocortin (MC) receptors, There is increasing evidence that th e MG receptor subtype 1 (MC-1R) is expressed in vitro by several other cuta neous cell types besides melanocytes and keratinocytes. Our knowledge on th e MC-1R expression in skin, however, remains fragmentary. In order to exami ne the expression of MC-1R in human skin cells in vitro and in situ, we mad e use of a recently described antibody directed against the amino acids 2-1 8 of the human MC-1R. Flow cytometry analysis revealed the highest MC-1R an tigenicity in normal melanocytes and keratinocytes, followed by dermal fibr oblasts, microvascular endothelial cells and WM35 melanoma cells. Little or no expression was detected in KB carcinoma cells and Fs4 fibroblasts. In n ormal human skin, immunoreactivity for the anti-MC-1R antibody was detected in hair follicle epithelia, Sebocytes, secretory and ductal epithelia of s weat glands, and periadnexal mesenchymal cells. Interfollicular epidermis w as largely unreactive in adult skin as opposed to undifferentiated keratino cytes of fetal skin. Our findings form a framework within which MC-1 recept or expression can be studied in various skin diseases.