Cold-storage of platelets followed by rewarming induces changes in Glycoprotein (GP) IbI?-distribution indicative of receptor clustering and initiates thromboxane A 2-formation. GPIbI? is associated with 14-3-3 proteins, which contribute to GPIbI?-signaling and in nucleated cells take part in apoptosis regulation.Objectives and methods: We investigated whether GPIbI?-clustering induces platelet apoptosis through 14-3-3 proteins during cold (4 h 0 A?C)-rewarming (1 h 37 A?C).Results: During cold-rewarming, 14-3-3 proteins associate with GPIbI? and dissociate from Bad inducing Bad-dephosphorylation and activation. This initiates pro-apoptosis changes in Bax/Bcl-x L and Bax-translocation to the mitochondria, inducing cytochrome c release. The result is activation of caspase-9, which triggers phosphatidylserine exposure and platelet phagocytosis by macrophages. Responses are prevented by N-acetyl-d-glucosamine (GN), which blocks GPIbI?-clustering, and by O-sialoglycoprotein endopeptidase, which removes extracellular GPIbI?.Conclusions: Cold-rewarming triggers apoptosis through a GN-sensitive GPIbI?-change indicative of receptor clustering. Attempts to improve platelet transfusion by cold-storage should focus on prevention of the GPIbI?-change. A? 2010 International Society on Thrombosis and Haemostasis.