Ultraviolet-B irradiation of platelets induces a dose-dependent increase in the expression of platelet activation markers with storage.

Ultraviolet B (UVB) irradiation of platelet concentrates (PCs) has been proposed as a novel technology to prevent HLA sensitization. We have recently reported that 2 J/cm2 of UVB radiation abolishes alloreactive lymphocyte responses in vitro. In order to increase the efficacy of UV irradiation for the prevention of HLA sensitization, we exposed PCs to 4 or 8 J/cm2 of UVB and evaluated the effect of UV radiation on platelet integrity during storage. We report here that UV exposed platelets show a progressive increase in the expression of activation markers P-selectin (GMP-140; CD62) and LIMP-CD63 (GP-53; CD63) on the platelet membrane over time in a dose-dependent manner compared to age-matched controls. Platelet metabolism was also enhanced as evidenced by significant changes in lactate and pH during post-irradiation storage. Based on these findings we transfused PCs within 4 h after UV irradiation. PCs exposed to 4 J/cm2 showed normal post-transfusion recoveries and haemostatic functions, while poor platelet recoveries were found after administration of PCs exposed to 8 J/cm2. We hypothesize that the rapid expression of P-selectin on platelets exposed to the higher dose of UVB leads to an increased binding of these platelets to leucocytes in the circulation resulting in poor platelet recoveries.