Expression of OKM5 antigen on epidermal cells in mycosis fungoides plaque stage.

To characterize and quantitate potential antigen-presenting cell subsets in the epidermis of patients with cutaneous T-cell lymphoma, epidermal cells in suspension were obtained from involved and uninvolved skin. Involved epidermis contained increased numbers of OKT6+HLA-DR+ Langerhans cells and a variable number of OKM5+ epidermal cells (ECs) in all mycosis fungoides (MF) patients tested (N = 14). The OKM5+ EC population from involved epidermis of MF patients were heterogeneous and comprised both OKM5+HLe1- keratinocytes and OKM5+HLe1+ leukocytes. Uninvolved epidermis, in 6 of 14 patients with MF, contained a small number of OKM5+ leukocytes; however, no OKM5+ keratinocytes were detected. Neither OKM5+ leukocytes nor OKM5+ keratinocytes were detected in the epidermis obtained from healthy controls. The increased number of potential antigen-presenting cells, that is, OKT6+HLA-DR+ Langerhans cells and OKM5+HLA-DR+ monocytic leukocytes, in the epidermis of patients with MF may be important for the activation of abnormal T cells contained within the epidermis of these patients. Such activated T cells may release gamma-interferon and induce expression of both HLA-DR and OKM5 antigens on keratinocytes. OKM5+ keratinocytes are present in the epidermis of patients with MF, but not in normal skin, and may thus play a role in the pathogenetic mechanisms of mycosis fungoides by recruitment of immunocompetent cells to the epidermis.