Immunohistochemical demonstration of the expression of neurofilament proteins in Merkel cells.

The presence of immunoreactive neurofilament proteins has previously been reported in Merkel cell carcinomas but not in normal human epidermal and dermal Merkel cells. We have studied the immunoreactivity of epidermal Merkel cells for neurofilament triplet proteins (68 KD, 70 KD, 160 KD, 200 KD), using epidermal sheets prepared from the plantar skin of human adults, which enabled us to survey large numbers of Merkel cells. Neurofilament protein 200 KD-positive cells were readily identified, while neurofilament protein 68 KD-, 70 KD- and 160 KD-positive cells were largely absent. 200 KD-positive cells in the epidermis were confirmed to represent Merkel cells by a sequential immunoenzyme labeling for the simple epithelial type cytokeratin (No. 8). 200 KD-positive cells were 5.9% of the total number of epidermal Merkel cells. Despite a heterogeneous expression of neurofilament protein subspecies between the normal and transformed Merkel cells, the presence of neurofilament proteins in epidermal Merkel cells may link them to Merkel cell carcinomas.