DIFFERENTIAL INDUCTION OF P-SELECTIN EXPRESSION ON PLATELETS BY 2 CELL SEPARATORS DURING PLATELETPHERESIS AND THE EFFECT OF GENDER ON THE RELEASE OF SOLUBLE P-SELECTIN

BACKGROUND: Though a number of studies have elegantly characterized pl atelet activation during storage, less attention has been paid to the initial activation caused by different collection procedures. STUDY DE SIGN AND METHODS: The effects of two blood cell separators on the init ial activation of platelets were measured by flow cytometric analysis of P-selectin expression in 13 male donors on one cell separator (CS 3 000 Plus) and 11 men and 9 women on the other (MCS 3P). In addition, t he storage and release of soluble P-selectin (circulating P-selectin [ cP-selectin]) by platelets were quantified, to determine whether the c hange in cP-selectin is a more sensitive marker for initial platelet a ctivation, and the influence of gender on measured endpoints was evalu ated. 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 preapher esis cP-selectin levels were compared to those in apheresis PCs, cP-se lectin increased from 51 to 101 ng per mL in plasma of CS 3000 Plus PC s, whereas cPselectin 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<0.00 5 for all). The relative increase in cP-selectin was higher in women t han in men in MCS 3P PCs (p = 0.013). Concomitantly, the amount of P-s electin stored in platelets before apheresis decreased (p<0.025 for al l). 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 a ctivation of platelets obtained with the MCS 3P is less than that of p latelets obtained with the CS 3000 Plus; 2) that the increase in cPsel ectin 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 st imulus. Differences in platelet activation by various cell separators and the sex of the donor may contribute to variability of PC quality.