Epidermal T lymphocytes and HLA-DR expression in psoriasis.

Double staining immunofluorescent techniques and monoclonal antibodies were used to study the numbers, distribution, HLA-DR expression and relationship of T-cell subpopulations and dendritic cells in psoriatic skin. In the dermis there was a definite increase in both T helper and T suppressor cells in uninvolved skin of psoriatic patients, and the appearance of clinical lesions was not associated with any detectable change in the numbers of these cells in the dermis. In contrast, eruption of skin lesions was associated with an increase in the numbers of epidermal HLA-DR+ dendritic cells and also with epidermal influx and activation of T helper cells, while resolution of lesions coincided with increased epidermal entry and activation of T suppressor cells. Both the T helper and T suppressor cells were preferentially found adjacent to epidermal dendritic cells. These findings suggest that the clinical activity of psoriasis may be dependent upon the interaction of T helper and suppressor cells with antigen-presenting cells in the epidermis.