Lymphocytes treated by extracorporeal photopheresis demonstrate a drop in the Bcl-2/Bax ratio: A possible mechanism involved in extracorporeal-photopheresis-induced apoptosis

Background: Recently, apoptosis has been identified in treated lymphocytes, prior to their re-infusion, when tested ex vivo. Previous work has demonstrated a close association between the genes p53, Bcl-2 and Bax and apoptosis induced by UV irradiation. Objectives: We wanted to establish whether the expression of the protein product of these genes was altered in lymphocytes treated with extracorporeal photopheresis (ECP) prior to re-infusion and therefore possibly implicated in the early apoptosis observed. Method. Lymphocytes were isolated immediately before treatment and immediately prior to re-infusion and tested for intracellular levels of p53, Bcl-2 and Bax proteins. Results: No increase in p53 expression was observed at re-infusion; however, the mean fluorescent intensity ratio of the apoptotic inhibitor protein Bcl-2 to the apoptosis-inducing protein Bax dropped significantly. Conclusion: The early apoptosis observed in ECP-treated lymphocytes at re-infusion might be attributed to dysregulation in the expression of the apoptotic genes Bcl-2 and Bax. Copyright (C) 2002 S. Karger AG, Basel.