EFFECT OF WHITE CELLS ON PLATELETS DURING STORAGE

White cells (WBCs) present in stored platelet concentrates have adverse effects on platelet function and on posttransfusion recovery. Although these effects have been attributed to the fall in pH that results from active WBC metabolism, platelets stored in gas‐permeable storage bags still exhibit abnormalities, despite maintenance of a stable pH of greater than 6.0. The changes in platelet proteins and function brought about by storage with a controlled number of WBCs were studied. Twelve platelet‐pheresis specimens were centrifuged at 180 x g to achieve a WBC count of less than 2 times 105 per mL (which contained less than 10% granulocytes). These specimens were split into two aliquots and placed in platelet bags for storage at 22° C with constant horizontal agitation. Neutrophils, obtained from the same donor by centrifugation of 50 mL of whole blood through a discontinuous ficoll gradient, were added to one of the two platelet storage bags to achieve a final neutrophil count of 1 times 106 per mL. Platelet aliquots were removed and studied on Days 3 and 5. In platelets stored without neutrophils, the average response to ristocetin, using the mean slope as an index of platelet responsiveness, was 10.3 (n = 9, SD = 11) on Day 3, whereas for the platelets stored with neutrophils, it was 1.25 (n = 12, SD = 0.9, p<0.01). Significant differences were also seen on Day 5 (slope = 4.5 for platelets stored without neutrophils, slope = 0.3 for platelets stored with neutrophils, p<0.01). Platelet aggregation with 8 μM ADP and 1.5 mg per mL of collagen did not differ significantly. In four similar experiments using lymphocytes (107/mL) instead of neutrophils, no significant change in platelet function was noted. Platelet lysates of similar protein concentration, analyzed by polyacrylamide gel electrophoresis and stained with Coomassie blue, showed decreased or absent staining of a band of molecular weight of 170,000 in platelets stored with neutrophils, as compared to control. Immunoblot analysis of seven sets of platelet lysates using antiserum to glycocalicin, a fragment of glycoprotein Ib (GPIb), demonstrated decreased staining at molecular weight of 140,000 in the platelets stored with neutrophils by Day 3 of storage. Platelets stored for 3 days at 22° C with 106 per mL of neutrophils showed decreased responsiveness to ristocetin, decreased quantities of GPIb, and decreased amounts of a 170‐kDa protein with electrophoretic properties similar to thrombospondin. These findings are consistent with proteolysis of GPIb by one of the neutrophil proteolytic enzymes. 1990 AABB