The merkel cell in human epidermis: its differentiation from other dendritic cells

Abstract

Until recently, Merkel cells were not consistently identified as the third dendritic cell in human epidermis, because light microscopy and low power electron microscopy did not readily allow the differentiation of Merkel cells from the other two dendritic cells of the epidermis (e.g. the melanocyte and the Langerhans cell). In an electron microscopic study where special attention was given to dendritic cells in human epidermis by higher power magnification, Merkel cells were characterized by the specific Merkel cell granules and fine intracytoplasmic filaments inserted into an occasional Merkel cell desmosome. Use of these criteria permitted definite differentiation of Merkel cell from melanocytes and Langerhans cells, as the latter have neither the typical Merkel cell granules nor fine filaments and desmosomes. The proximity of an epidermal neurite above the basal lamina or of a dermal neurite close to the basal lamina, further aided the detection and differentiation of Merkel cells in human epidermis. Preliminary evidence suggests that Merkel cell granules may contain catecholamines. Thus, the easy identification of Merkel cells by high power electron microscopy raises interesting questions for the role of this cell and its apparent catecholamine content in pathological states of the skin.