Variations in S-100 protein expression in naevocellular naevi may be related to metabolic activity

Significant amounts of S-100 protein were demonstrated in naevus cells by an immunoperoxidase technique. Distribution of S-100 protein was similar in the various types of naevi tested. In most lesions, the superficial A-type naevus cells stained most heavily, while staining was weaker in the deeper B- and C-type naevus cells. The intensity of staining was not, however, homogeneous in the cells of the various layers of the naevus. S-100 protein was especially abundant in giant naevus cells which occurred in the vicinity of sub-epidermal A-type naevocytes. Cells from neurocutaneous melanosis contained extremely large amounts of S-100 protein. Normal melanocytes in the epidermis over dermal naevi contained variable amounts of S-100 protein, but mainly showed weak staining. However, in the basal epidermis of traumatized naevi there were many unusually large and partly dendritic melanocytes. In this part of the epidermis, S-100 protein-positive cells lay close together, and many stained strongly. In earlier work, large amounts of metabolic enzymes were found at the same sites in traumatized naevi and giant cells. These results suggest that a high degree of expression of S-100 protein is due to metabolic activity shown, for example, by giant naevus cells and basal melanocytes of the regenerating epidermis over traumatized naevi.