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INHIBITION OF CONTACT HYPERSENSITIVITY REACTION IN MICE INDUCED BY PREVIOUSLY PHOTOOXIDIZED PSORALEN N. A. Yurikova, E. S. Andina, M. B. Neklyukova, A. A. Kyagova and A. Ya. Potapenko Department of Medical and Biological Physics, Russian State Medical University, Ostrovityanova street 1, Moscow 117869, Russia. Telefax: (095)2451220, E-Mail: apotap@mx.iki.rssi.ru Abstract Psoralens, together with ultraviolet 1ight A (PUVA), are used for the treatment of the series of T cell mediated diseases. The role of photooxidative reactions in psoralen phototherapy is not entirely clear. It was shown that the products of psoralen photooxidation (POP) influenced the delayed type hypersensitivity (DTH) reaction in mice. We investigated the effect of psoralen photooxidation products on the functions of the T-cell immunity in mice by assessing the contact hypersensitivity (CHS) reaction to two haptens: 2,4-dinitrofluorobenzene (DNFB) and trinitrochlorobenzene (TNCB). We found that, being intravenously injected, POP induced inhibition of the CHS reaction to both haptens used. It was revealed that POP inhibited CHS reaction significantly on the afferent phase of immune response. Probably, psoralen photooxidation products may be used for the therapy of some hyperproliferative T cell mediated diseases.