Monoclonal antibody MAC 387 recognizes a myelomonocytic antigen shared by epithelial cells in inflammatory skin diseases.

The monoclonal antibody MAC 387 recognizes an antigen expressed by human macrophages and granulocytes. Normal epidermis does not react with the antibody, but the inflamed epidermis may react. In this immunocytochemical study we have investigated the intracytoplasmic expression of the MAC 387 antigen in biopsies of a variety of skin disorders. In lichen planus the basal cells were usually negative, whilst suprabasal cells were positive. In the majority of other inflammatory dermatoses studied, there was positive staining of basal and suprabasal cells. A parallel frozen- and paraffin-section study of biopsies of cutaneous T-cell lymphomas and inflammatory conditions failed to demonstrate HLA Class II expression in the cytoplasm of keratinocytes. Expression of the MAC 387 antigen in the epidermis is directly associated with cell-mediated activity in the papillary dermis, but is not related to HLA Class II expression.