Background: Though a number of studies have elegantly characterized platelet activation during storage, less attention has been paid to the initial activation caused by different collection procedures.
Study design and methods: The effects of two blood cell separators on the initial activation of platelets were measured by flow cytometric analysis of P-selectin expression in 13 male donors on one cell separator (CS 3000 Plus) and 11 men and 9 women on the other (MCS 3P). In addition, the storage and release of soluble P-selectin (circulating P-selectin [cP-selectin]) by platelets were quantified, to determine whether the change in cP-selectin is a more sensitive marker for initial platelet activation, and the influence of gender on measured endpoints was evaluated.
Results: The CS 3000 Plus increased the percentage of P-selectin-positive platelets from a median of 3.4 percent before apheresis to 7.6 percent (p = 0.006) in platelet concentrates (PCs), whereas the MCS 3P did not (p = 0.002 between the two cell separators). When preapheresis cP-selectin levels were compared to those in apheresis PCs, cP-selectin increased from 51 to 101 ng per mL in plasma of CS 3000 Plus PCs, whereas cP-selectin levels increased from 53 to 78 ng per mL in MCS 3P PCs (men) and from 48 to 99 ng per mL in MSC 3P PCs (women) (p<0.005 for all). The relative increase in cP-selectin was higher in women than in men in MCS 3P PCs (p = 0.013). Concomitantly, the amount of P-selectin stored in platelets before apheresis decreased (p<0.025 for all). When donors undergoing apheresis on the MCS 3P were compared, the amount of P-selectin stored in the platelets of PCs was higher in men than women (p = 0.026).
Conclusion: This trial shows 1) that initial activation of platelets obtained with the MCS 3P is less than that of platelets obtained with the CS 3000 Plus; 2) that the increase in cP-selectin is a more sensitive marker for initial platelet activation than the expression of P-selectin on the surface; and 3) that the relative amount of cP-selectin is higher in women than in men given the same stimulus. Differences in platelet activation by various cell separators and the sex of the donor may contribute to variability of PC quality.