The human peripheral lymphocyte--a model system for studying the combined effect of psoralen plus black light

The effect of psoralen plus long wavelength ultraviolet light (UVA) on 3H-thymidine uptake of PHA stimulated human lymphocytes was investigated. PHA induced lymphocyte transformation was inhibited by the combined action of psoralen and UVA irradiation in a dose related manner. Inhibition of DNA-synthesis occurred at concentrations of psoralen that can be expected in the serum of patients treated by systemic photochemotherapy. No effect was noted at these psoralen concentrations in the absence of UVA irradiation. Also did UVA irradiation in the absence of psoralen not inhibit 3H-thymidine incorporation into PHA stimulated lymphocytes.