Increased platelet surface expression of p-selectin and thrombospondin as markers of platelet activation in essential thrombocythaemia

Essential thrombocythaemia (ET) is a clonal myeloproliferative disorder ass ociated with an increased risk of both thromboembolic and bleeding complica tions. Platelet activation plays a crucial role in the pathogenesis of pret hrombotic conditions. The platelet surface expression of p-selectin (CD62p) and thrombospondin (TSP) has been shown to correlate with platelet activat ion. In the present study, we used a flow cytometric assay to study whether the fraction of platelets expressing CD62p and TSP is increased in newly d iagnosed ET. Thirty-four patients with newly diagnosed ET and 25 healthy co ntrol subjects were investigated. The proportion of platelets expressing th e activation-dependent antigens CD62p and TSP was higher in patients with E T (CD62p: 14.7 +/- 15.0%; TSP: 12.4 +/- 9.9%) as compared with healthy cont rol subjects (CD62p: 3.0 +/- 4.0%: TSP: 3.2 +/- 3.2%; p< 0.001). In ET, the re was a linear correlation between platelet surface expression of CD62p an d TSP (p<0.0001, r=0.83). At diagnosis of ET, 20 patients were symptomatic and 14 asymptomatic. Compared with asymptomatic ET patients there was no di fference in the expression of CD62p (18.3 +/- 16.2% vs. 14.5 +/- 13.4%) and TSP (14.4 +/- 9.8% vs. 12.8 +/- 9.5%) in symptomatic ET patients. In concl usion, increased expression of platelet neoantigens is present at the diagn osis of ET. Both activation-dependent epitopes CD62p and TSP are increasing ly expressed on the platelet surface in newly diagnosed ET patients. (C) 19 99 Elsevier Science Ltd. All rights reserved.