Deficiency of platelet ERp57 impairs activation of αIIbβ3 and platelet aggregation. (A) ERp57-deficient platelets have a defect in activation of αIIbβ3 (detected by the JON/A activation dependent antibody). Depicted is a representative sample and the mean fluorescent intensity (MFI) of cumulative data ± SE (n = 5). (B) Representative aggregation tracing and combined results (n = 6) showing the aggregation defect in ERp57-deficient platelets using convulxin (300 ng/mL). (C) Correction of the aggregation defect of Pf4-Cre/ERp57fl/fl platelets by addition of ERp57 relative to ERp57fl/fl control platelets. Additional experiments show correction of the aggregation defect in ERp57-deficient platelets by addition of 50 or 100 nM ERp57 (n = 3 for each condition). Recombinant ERp57 was added for 5 minutes before aggregation was induced by convulxin (150 ng/mL).