Ionising Irradiation Influences Platelet Adhesion and Aggregation under High Flow Conditions.

Transfusion-associated graft-versus-host disease (GVHD) is a dramatic immunologic reaction mediated by transfused immunocompetent lymphocytes directed against an immunocompromised host. GVHD shows a rapid onset and is characterized by severe symptoms and a poor response to treatment (mortality rate > 90%). Prophylactic gamma irradiation of cellular blood components is the most efficient and reliable way to prevent GVHD. The currently recommended standard dose of gamma irradiation of blood products is 25 Gy. While irradiated blood components including platelet concentrates have been extensively transfused over the past 25 years, only few studies (with controversy results) evaluated the effect of ionising irradiation on platelet morphology and function. In this study, we examined the effect of a standard irradiation dose of 25Gy on platelet function using a platelet function analyzer (PFA-100). Citrate-anticoagulated blood was obtained in duplicate from twelve healthy blood donors. One sample was immediately irradiated according to a standard protocol (25 Gy), the other specimen was used as control. Platelet function of irradiated and control samples was evaluated using PFA-100. This device applies a high shear flow system to simulate the conditions under which platelets are subjected at the site of a damaged blood vessel wall. Anticoagulated whole blood was passed through the membranes coated with either collagen and epinephrine (Col/Epi) or collagen and ADP (Col/ADP) under hemodynamic conditions similar to those of small capillaries. Platelets adhere and aggregate across the aperture until the flow ceases, evaluated by the closure time (CT, sec). Statistical analysis was performed using a standard software (Sigma Plot v. 8; Student’s paired t test). Analysis of platelet function with Col/Epi cartridges showed that irradiated samples had a prolonged closure time compared to corresponding non irradiated controls (144 ± 21 sec vs. 120 ± 18 sec, p<0.05). The averaged CT prolongation was 19±5%. Analysis of CT using Col/ADP cartridges showed also prolongated CT (averaged prolongation 7%) in seven of nine irradiated samples compared to non irradiated controls (97 ± 14 sec vs. 103 ± 13 sec, p<0.05). Our results suggest that a standard dose of ionising irradiation for prevention of GVHD has a significant influence on platelet function. The biochemical nature by which this platelet dysfunction following irradiation is caused, remains to be assessed in further detail.