Detection of ACTH, MC‐1R and MC‐4R immunoreactivity in human terminal and vellus hair follicles

Pro‐opiomelanocortin (POMC) peptides such as ACTH and α‐MSH play an important role in the pigmentation of human skin and hair. Both peptides bind to a family of transmembrane receptors known as the melanocortin receptors (MC‐Rs). To investigate the in situ expression of α‐MSH, ACTH and MC‐Rs, we performed immunohistochemical studies on human terminal and vellus hair follicles. Immunoreactivity for ACTH, MC‐1R and MC‐4R was detected in both human terminal and vellus hair follicles, with a pronounced increase of staining intensity in the suprabulbar and bulbar region of anagen hair follicles. The MC‐1R immunoreactivity in situ was in accordance with in vitro studies showing expression of MC‐1R at the RNA level in human hair follicle keratinocytes. There was no detectable difference in the staining pattern of strong, pigmented terminal hair follicles as compared with fine, silky and non‐pigmented vellus hair follicles. These results indicate that POMC‐derived peptides may play a regulatory role in the human hair follicle independent of the pigmentation process. The expression pattern of ACTH and its receptors MC‐1R and MC‐4R in the human hair follicle correlates with the immune privilege of the human hair follicle which is characterized by the absence of immune cells in the bulbar region of anagen hair follicles. Thus, ACTH may possibly be involved in the maintenance of the peribulbar immune privilege in both, terminal and vellus hair follicles.