Release of Procoagulant and Proinflammatory Cell-Derived Microparticles (MP) During Blood Storage: Effects of Storage Time, Leukoreduction, and Residual Platelets,

Several studies have indicated that transfusion with older blood carries more risk of adverse reactions than transfusion with younger blood, but this remains controversial. It is not clear why older blood may carry increased risks, or what the “safe age” of stored blood is. It is known that multiple bioactive substances are generated from blood during storage, and one or more of these substances may be involved in transfusion-related complications. Among them, MP are a recognized marker of the storage lesion, and their involvement in transfusion-related complications has been postulated. However, questions such as MP species, quantity, biological activity, and factors affecting their release are not well elucidated. The purpose of this study was to quantify MP species and their activity in stored RBC as a function of storage time, and to evaluate the impact of leukoreduction and residual platelets on MP release.

(I) MP generation and functional activity Thirty-four bags of packed RBC (16 non-leukoreduced, 18 leukoreduced) of known blood types (A+, B+, AB+, O+) were obtained from the blood bank within 2–4 days of drawing, and then stored at 4°C. Time of receipt was defined as day 0. At days 0, 10, 20, 30, and 40, 40 mL samples were centrifuged at 1000xg for 20 min to remove cells. The supernatants were then assayed for: (1) subtypes of MP by flow cytometry comprising (a) red cell MP (RMP) assessed by CD235a, (b) leukocyte MP (LMP) by CD45, (c) platelet MP (PMP) by CD41, (d) endothelial MP (EMP) by CD144, and (e) generic MP by Ulex Europaeus (Ulex) or Annexin V (AnV); (2) MP-mediated thrombin generation assay (TGA); (3) MP-mediated inflammatory activity by CD 11b expression in neutrophils following incubation with MP. (II) Reconstitution of increasing platelet counts in leukoreduced RBC. To investigate the effect of residual platelets on RMP generation, we mixed a constant amount of RBC with increasing amounts of type-matched platelets (0 to 250,000/μL f.c.) in standard storage bags and measured time-dependent MP release.

(A) Time-course of MP generation (i) Non-leukoreduced. RMP, PMP and LMP all increased with time, but with different patterns. RMP increased little to day 10 but then rose exponentially, and by day 40 they were 4–6 fold higher than at day 0. PMP counts rose steadily from day 0 and peaked at day 20, being 2–3 fold higher than at day 0. LMP showed no significant change until day 20 when they started to increase, and then increased sharply after day 30, and by day 40 were 1.5–2 fold higher than at day 0. Levels of PMP (days 0 to 20) and RMP (days 20 to 40) correlated with increasing MP-mediated procoagulant and inflammatory markers. (ii) Leukoreduced. Pre-storage leukoreduction decreased RMP generation by 20–40%, completely suppressed PMP and LMP generation, and reduced total MP-mediated procoagulant and inflammatory markers by 40–60%. CBC showed that leukoreduction not only removed >99% WBC but also reduced residual platelets by >95% (from 90 ±30 ×10³/μL to 3.5 ±1.3 ×10³/μL). This suggests that residual leukocytes and platelets potentiate RMP generation. (B) Effects of residual platelets on RMP generation. To further study the effects of platelets on RMP generation, we mixed known counts of platelets with leukoreduced RBC, and then evaluated RMP generation over time. We found that RMP levels released were proportional to the platelet counts, as were the procoagulant and inflammatory markers. These results show that platelets in stored RBC play a key role in RMP generation.

Multiple MP types (PMP, LMP, RMP) are released during storage, and their levels increase over time but their patterns of change are different. Procoagulant and inflammatory markers increase in parallel with PMP and RMP. Our data support the hypothesis that age of stored blood could be important in transfusion-related complications, via MP production. Leukoreduction sharply reduces MP generation and procoagulant and inflammatory markers, suggesting that known benefits of leukoreduction may be attributable to reduced MP production. The finding that residual platelets in stored RBC can potentiate RMP generation suggests that minimizing platelets in non-leukoreduced packed cells could reduce the risk of transfusion-related complications. (Supported by NIH grant 1R01HL098031).

No relevant conflicts of interest to declare.