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HLA‐DR expression on keratinocytes is a common feature of diseased skin

Biopsy specimens from 185 patients with 52 different skin disorders were investigated by indirect immunofluorescence staining for the presence of HLA‐DR bearing keratinocytes and their association with an underlying inflammatory infiltrate and in particular with activated (HLA‐DR‐positive, Leu‐4‐positive) T lymphocytes. HLA‐DR expression on keratinocytes was demonstrated in 38 dermatoses, including lymphocytic vasculitis, lupus erythematosus, morphea, vitiligo, lichen planus, cutaneous T‐cell lymphoma, various infectious dermatoses, allergic contact dermatitis, granulomatous dermatoses, Sweet's syndrome, lichen sclerosus and erythema nodosum. In 27 of these this had not previously been reported. Occurrence of HLA‐DR on keratinocytes was invariably linked to the presence of a lymphocytic infiltrate containing numerous activated T‐cells (Leu‐4+, HLA‐DR+) whereas such infiltrates were not accompanied by HLA‐DR expression on keratinocytes in all the dermatoses investigated, as in pseudolymphoma and erythema anulare centrifugum. However, HLA‐DR positive keratinocytes were consistently absent in skin disorders lacking any significant lymphocytic infiltration (e.g. leukocytoclastic vasculitis, bullous autoimmune dermatoses, genodermatoses and mastocytosis). Although it has been suggested that HLA‐DR‐positive keratinocytes are involved in various immune responses of the skin, their exact functional significance is, as yet, unknown.