PRODUCTION OF HYDROGEN-PEROXIDE BY CUTANEOUS T-CELL LYMPHOMA FOLLOWING PHOTOPHERESIS WITH PSORALENS AND ULTRAVIOLET-LIGHT

Treatment of peripheral blood mononuclear cells with 8-methoxypsoralen (8-MOP) and ultraviolet light, a procedure known as PUVA, has been found to be useful in the management of systemically disseminated cutaneous T-cell lymphoma (CTCL). In the present study we used a highly sensitive flow cytometric assay in conjunction with the hydroperoxide-sensitive dye 2',7'-dichlorofluorescein diacetate to measure intracellular hydrogen peroxide in normal lymphocytes and CTCL following PUVA treatment. Based on their laser light-scattering properties, lymphocytes were separated into three major subpopulations. We found that ultraviolet light alone caused an increase in the hydrogen peroxide content of each of the subpopulations, a response that was augmented when the cells were pretreated with 8-MOP (50 ng/ml). Cells from CTCL patients were more sensitive to the effects of 8-MOP than were normal lymphocytes. In both cell types, the production of hydrogen peroxide was found to be inhibitable by catalase. We noted an increase in hydrogen peroxide production following photopheresis; however, this was observed only 24 h after treatment. In addition, a further increase in hydrogen peroxide production was observed in lymphocytes isolated from peripheral blood that had been obtained from patients at 15 min after a second photopheresis treatment. Hydrogen peroxide is known to modulate the action of cytokines as well as the immunological responses of leukocytes. Our data suggest that the production of hydrogen peroxide by lymphocytes may be important in the action of PUVA in CTCL.