Immunopathologic study of lichenoid skin diseases: correlation between HLA-DR-positive keratinocytes or Langerhans cells and epidermotropic T cells.

Skin biopsy specimens from 24 patients with different lichenoid skin diseases that had been proved histologically were studied immunohistologically. Marked differences were noted in the number of OKT6+/S100+ Langerhans cells within the epidermis and dermis in the lesional skin between lichen planus (and its related disease) and lupus erythematosus; in the former these cells were increased in number; in the latter they were decreased in number compared with those in uninvolved perilesional skin. Human lymphocyte antigen (HLA)-DR expression on keratinocytes was observed not only in lichenoid skin diseases but also in control cases without epidermal involvement. In the two cases of systemic lupus erythematosus, the uninvolved perilesional skin also show weak and focal HLA-DR reactivity in the basal layer. HLA-DR+ keratinocytes could play an important role at least in the perpetuation of epidermal cell damage mediated by T cells.