Comparison of soluble CD40L concentrations and release capacities in apheresis and prestorage pooled platelet concentrates.

Introduction: Soluble CD40L (sCD40L) is expressed by platelets and is involved in the stabilization of arterial thrombi. Additionally, it was shown that sCD40L accumulation occurred in stored blood products triggering adverse transfusion reactions like TRALI. To study the influence of the preparation technique on sCD40L accumulation and platelet function we examined CD40L concentrations in prestorage pooled platelet concentrates compared to apheresis products. In addition, sCD40L release capacity was determined as a marker for platelet viability. Material and methods: sCD40L concentrations were determined in prestorage pooled platelet concentrates (n = 8) and in platelet apheresis concentrates (n = 8) before and after platelet stimulation (recalcification and clot formation) at day 1, 3 and 5 under routine storage conditions. sCD40L concentrations were determined by a commercially available ELISA kit. Results: sCD40L concentrations in storage medium increased over time in prestorage pooled platelet concentrates (from 1,185 pg/mL +/- 87 pg/mL at day 1 to 4,464 pg/mL +/- 212 pg/mL at day 5) as well as in apheresis products (from 581 pg/mL +/- 124 pg/mL at day 1 to 2,718 pg/mL +/- 154 pg/mL at day 5) in a hyperbolic manner. Recalcification and clot formation caused an increase in sCD40L concentrations (for example 3,842 pg/mL +/- 769 pg/mL before platelet activation to 31,219 pg/mL +/- 2,063 pg/mL after platelet activation at day 3), and we observed comparable release capacities for both preparation techniques, however, decreasing over storage time up to 50% (day 5) of the respective control value (day 1). Conclusions: Amounts of sCD40L accumulation and release capacity during storage of platelet concentrates were dependent on storage duration, but showed no relevant differences regarding the preparation technique. After 5 days of storage, CD40L basal levels were increased, in contrast sCD40L release capacity was decreased. By recalcification and clot formation sCD40L release capacity could be easily induced and is assumed to be used as a marker for platelet viability.