The activation of Langerhans cells in oral lichen planus.

The numbers of CD1, HLADR, HLADP and HLADQ positive, intraepithelial, dendritic cells were compared in lesions of oral lichen planus and normal oral mucosa using an immunoalkaline phosphatase technique. In normal mucosa, there were equal numbers of CD1 and HLADR positive cells but significantly fewer cells were positive for HLADP (P less than 0.001) and HLADQ (P less than 0.05). In lichen planus, the cells appeared more dendritic and equal numbers of CD1, HLADR, HLADP and HLADQ positive cells were found, with significantly more HLADP (P less than 0.01) and HLADQ (P less than 0.05) positive cells than in normal mucosa. There was no change in the number of CD1 and HLADR positive cells. These results show that although there is no change in the total number of Langerhans cells (CD1 positive cells) in lichen planus, there is an increase in Class II major histocompatibility antigen expression. This suggests that in lichen planus, Langerhans cells are immunologically active and play a role in lesion development.