Abstract: Although application of topical psoralen followed immediately by ultraviolet-A irradiation (non-interval PUVA) was reported to be effective in the treatment of psoriasis, its precise mechanisms of action have not yet been explored. Since regular topical PUVA therapy, consisting of topical application of psoralen followed by UVA exposure 1-2 h later, can change the number and morphology of Langerhans cell (LC) and inhibit contact hypersensitivity (CHS). We investigated Whether these same effects may be induced by non-interval PUVA in experimental animals. Our resulos showed that no differences exist between these two types of PUVA treatment. Non-interval PUVA treatment of 3J/cm² produced no erythematous reactions and resulted in changes in the number and morphology of LC. The non-interval regimen also inhibited CHS to DNFB applied to the treated skin by inducing the suppressor lymphocytes. We also discussed the carcinogenic potential by non-interval PUVA.

Key words: PUVA therapy, Langerhans cell, Dermatitis, contact