Melanin-forming Schwann cells in some oral mucosal lesions.

Normal oral mucosa and some mucosal lesions show melanin pigmentation, and it is usually assumed that melanin-containing cells in the lamina propria are melanophages. In a study of oral mucosa from two cases of lichen planus and tow of sublingual keratosis, many brown, intracellular, Masson-Fontana-positive granules were seen. At the ultrastructural level some of the melanin-containing cells displayed characteristics of Schwann cells rather than melanophages. These cells were surrounded by a basal lamina and contained unmyelinated axons. Although the majority of the melanin granules in these cells were compound melanosomes, single melanosomes and premelanosomes were also seen. These findings show that in sublingual keratosis and oral lichen planus lesions some of the melanin-containing cells in the connective tissue may be melanin-forming Schwann cells.