Psoriasis infiltrating cell immunophenotype: changes induced by PUVA or corticosteroid treatment in T-cell subsets, Langerhans' cells and interdigitating cells.

The effects of PUVA or corticosteroid treatment on the distribution pattern of immunocompetent cells in psoriasis symptomatic skin were investigated. A total of 29 biopsies, taken before and a regular intervals during treatment, were studied in a two-stage immunoperoxidase technique using monoclonal antibodies directed against T cells, their major subsets, interdigitating cells, and Langerhans' cells. T cell exocytosis was not affected by PUVA or corticosteroid treatment. Instead, both treatment regimens led to an initial increase in interbasally localized T8+ suppressor/cytotoxic T cells. Increased T4/T8 ratios within the subepidermal infiltrates were restored to normal except in one case, who did not respond to PUVA-treatment. Epidermal and dermal T6+ Langerhans' cells decreased to almost absent. RFD1+ interdigitating cells had the same tendency, except in the PUVA-non-responding patient. Treatment of psoriasis with PUVA or corticosteroids thus results in a normalization of an initial immune imbalance in infiltrating immunocompetent cells. A working hypothesis on psoriasis immunopathogenesis and its restoration by treatment is presented.