Epidermal dendritic S100 positive cells in necrobiosis lipoidica and granuloma annulare.

Using an antibody to S100 protein, the number of dendritic cells above the basal layer in the epidermis was assessed in necrobiosis lipoidica and granuloma annulare. A statistically significantly higher number of these cells was found within the epidermis in necrobiosis lipoidica compared with granuloma annulare and normal skin. The numbers were similar to those seen in sarcoidosis and tuberculous reactions in the skin, which raises the possibility of an immune pathogenesis for necrobiosis lipoidica.