THE DISTRIBUTION OF MERKEL CELLS IN HUMAN FETAL AND ADULT SKIN

Merkel cells (MCs) have been a subject of investigation in human and animal studies for over a century, but their origin, function(s), and exact distribution in human skin remain largely unknown. The objectives of the present study were to quantify these cutaneous neuroendocrine cells in fetal and adult human skin, using an immunohistochemical marker (neuron-specific enolase) and morphometric methods. Our results indicate. that, in postnatal life, MC are sparsely distributed along the undersurface of epidermal and occasionally adnexal epithelium in an approximate range of 0.1-1.0 MCs per centimeter of basal zone. They are most numerous on volar skin and least on genital skin, and on the face they have a primarily perifollicular orientation. Fetal samples have shown that MCs appear between the 15th and 18th week of gestation and are most abundant on volar skin. They appear to arise within the epidermis, and are initially numerous and later diminish with increasing gestational age. Their predominance in intrauterine life suggests a functional role in growth and development.