There is no change in soluble leucocyte selectin concentrations in whole blood after 48 hours of storage at 4 °C.

Soluble leucocyte selectin (sL-selectin) is the plasma soluble counterpart of leucocyte-bound selectin (L-selectin). Bound L-selectin is responsible for early activation of leucocyte rolling during inflammation and is present on the surface of monocytes, lymphocytes and granulocytes. sL-selectin is a highly glycosylated protein that is cleaved by a membrane protease, predominantly from the surface of granulocytes, during cytokine activation of the cells (e.g. by interleukin[IL]-8, lipopolysaccharide, and granulocyte-macrophage colony-stimulating factor [GM-CSF])1–3. The soluble form of selectin displays biological activity via competitive inhibition, competing with its leucocyte-bound form for an endothelial ligand (a sialyl lewis X entity) activated by the cytokine tumour necrosis factor (TNF)-α1–3. Schleiffenbaum et al. were able to demonstrate an absolute concentration of sL-selectin needed to completely block leucocyte binding to activated endothelium (range: 8–15 μg/mL)2. sL-selectin has been shown to be quite stable with no significant decreases in plasma concentrations during storage at room temperature for 2–3 days, at 4 °C for 4 weeks, at −20 °C for 6 months and, probably, indefinitely at −70 °C3. sL-selectin circulates in normal plasma at an approximate concentration of 1.6 μg/mL (±0.8 μg/mL) and retains functional activity1,2. It has been suggested that this molecule may be a sensitive indicator of granulocyte activation and that it plays an important role in regulating leucocyte trafficking during inflammation1–8. Research on sL-selectin in certain disease states has shown a direct relationship between sL-selectin concentration and immunosuppressive effects1,2,4–10. Post-transfusion immunosuppression is considered to be a multifactorial phenomenon seen in patients who receive allogeneic transfusion therapies11–15. For example, it has been shown that the rates of graft survival are higher in transplant recipients who undergo allogeneic blood transfusions than in those who do not receive transfusions11. This phenomenon has also been noted in colorectal cancer surgery patients; those who received blood products had higher incidences of tumour regrowth and post-operative infections than those who did not require transfusions11,13–15. For this pilot study it was hypothesised that levels of sL-selectin in units of non-leucocyte-reduced whole blood from healthy donors would be elevated following 48 hours of storage at 4 °C. It was considered that mechanical manipulation, unit bag nutrient/preservative media and the blood storage process could activate granulocytes enough to cause active shedding of L-selectin. Since sL-selectin seems to function in the capacity of a sialyl lewis X ligand antibody, it is conceivable that a bolus of sL-selectin from donor blood could result in the binding of these ligands in the recipient and, therefore, prevent leucocyte rolling (and hence be a factor contributing to post-transfusion immunomodulation). A PubMed search conducted in March of 2014 revealed no studies addressing sL-selectin in transfusion products, or its relationship to post-transfusion immunomodulation/ immunosuppression. This study was approved by the Brooke Army Medical Center Institutional Review Board.