HLA-DR antigen expression on the keratinocyte surface in dermatoses characterized by lymphocytic exocytosis (e.g. pityriasis rosea).

We have investigated the immunoperoxidase staining pattern of the epidermis in several dermatoses characterized by exocytosis of mononuclear cells into the epidermis. We found that HLA-DR antigens showed an intercellular distribution in localized areas of the epidermis in nine of ten cases of pityriasis rosea, and in all four cases of spontaneously regressing flat warts, two cases of pityriasis lichenoides chronica, two of Schamberg's disease, and one case of lichen striatus. Lichen planus and mycosis fungoides cases were used as positive controls. OKT6 antigen was recognized only on the dendritic cells of the epidermis in all these cases. Judging from the distribution of Langerhans cells, the epidermal intercellular HLA-DR antigen seems to be expressed on the keratinocytes in such diseases, and this feature was confirmed by immunoelectron microscopy. These findings support the hypothesis that the expression of HLA-DR antigen on keratinocytes in these dermatoses is linked to cellular immune reactions involving the epidermis.