POPs generated by UVA and separated by HPLC induce cell death. (A) RP-HPLC elution profiles of a psoralen solution (2.7 mM) irradiated with increasing UVA doses (0-112 J/cm²). Jurkat cells (10⁶/mL) were incubated at 37°C in the presence of POPs (50 μM) generated by increasing UVA doses, as reported in panel A. After 20 hours, apoptosis was evaluated by appropriate changes of nuclei stained with Hoechst 33258 (B) or by staining with annexin V (C), whereas nuclear staining by PI was utilized for the evaluation of necrosis. Values are means ± SD of at least 4 experiments.