Microvesicles in platelet concentrates for transfusion.
The key objective of this study was to examine whether leucocyte depletion
generated or removed platelet-derived microvesicles in platelet concentrates for
transfusion. Three in-process leucocyte removal filters for pooled buffy coat derived
platelet concentrates, i. e. negative charged polyester, positively charged polyester, and
non-charged polyurethane, were compared. The effects of three major leucocyte
depletion technologies currently in use in the UK, i. e. Cobe LRS and Haemonetics
MCS+ LD apheresis, and filtration of pooled buffy coat derive platelets, on platelet
microvesiculation were also examined. Furthermore, the effects of various leucocyte
filters and leucocyte depletion technologies on platelet activation and the activation of
coagulation/complement systems were investigated. The procoagulant and anticoagulant
properties of microvesicles isolated from platelet concentrates were explored.
Leucocyte filtration of pooled bully coat derived platelet concentrates by all three
filters did not have a net effect on the level of microvesicles. All three leucocyte
depletion technologies gave similar values of microvesicles on day 1, but on day 5
MCS+ LD apheresis showed the lowest value, whilst Cobe LRS apheresis and buffy coat
methods were equivalent.
Among the three filters, the negatively charged filter activated the coagulation
system as measured by kallikrein-like and thrombin-like activities, but removed some
activated complement C3a, whereas the positively charged filter generated C3a. Among
the three leucocyte depletion technologies, platelets prepared by Cobe LRS showed the
lowest degree of activation of the coagulation system. However, both Cobe LRS and
MCS apheresis showed higher levels of C3a than filtered buffy coat derived platelets.
The microvesicles isolated from day 1 platelet concentrates could act as a
catalytic surface for both the coagulant and anticoagulant reactions as measured by the
formation of prothrombinase complex and the inactivation of FVa by activated protein C.
The microvesicles isolated from day 5 platelets showed an increased procoagulant
activity, whereas the anticoagulant activity substantially diminished.