Dose-effects of 8-methoxypsoralen and UVA in cultured human lymphocytes

Cultures of human lymphocytes were incubated with 8-methoxypsoralen (8-MOP) and irradiated with long wave ultraviolet light (UVA). Subsequently the mitogenic response to PHA was determined by 3H-thymidine incorporation. The minimal effective dosages of drug and light for the partial suppression of lymphocyte PHA-responsiveness were found to be 0.1 microgram/ml 8-MOP and 0.5 J/cm2 UVA. While an increase in the concentration of 8-MOP revealed a comparatively small rise in phototoxicity, a marked inhibition of 3H-thymidine uptake was obtained by increasing the UVA dosage. Cell viability of non-stimulated lymphocytes was similarly affected by the combined treatment.