Expression of MHC class II antigens (HLA DR, DP and DQ) by keratinocytes in oral lichen planus.

The incidence and distribution of keratinocytes expressing the major histocompatability complex antigens HLA DR, DP and DQ and their relationship to the density of the inflammatory infiltrate was determined in lesions of oral lichen planus and normal mucosa using an immunoalkaline phosphatase technique. Seven of eight biopsies of lichen planus showed evidence of keratinocyte HLA DR expression but the pattern was variable both within and between biopsies. A significant increase in density of lymphocytes was found beneath those areas showing HLA DR expression throughout the prickle cell layer compared with those areas showing patchy or no expression. No evidence for keratinocyte expression of HLA DP or DQ was found. These results suggest that expression of HLA DR by keratinocytes in lichen planus may be induced by the lymphocytic infiltrate perhaps as a result of interferon gamma production. The functional significance of such MHC Class II expression remains unknown.