Reduced β2-GPI is associated with increased platelet aggregation and activation in patients with prolonged isolated thrombocytopenia after allo-HSCT

We aimed to measure platelet function and its relationship with β2-GPI in prolonged isolated thrombocytopenia(PT) after allogeneic hematopoietic stem cell transplantation(allo-HSCT).Fifty-six patients with PT and 60 allo-HSCT recipients without PT(non-PT controls) were enrolled.Platelet aggregation and activation,β2-GPI and anti-β2-GPI antibody levels,vWF antigen,and vWF activity were analyzed.The effect of β2-GPI on platelet aggregation was also measured ex vivo.Results showed that ADP-induced platelet aggregation significantly increased(39%±7.5% vs.23%±8.5%,P=0.032),and the platelet expression of both CD62 p(33.6%±11.6% vs.8.5%±3.5%,P<0.001) and PAC-1(42.4%±7.6% vs.6.8%±2.2%,P<0.001) was significantly higher in patients with PT than in those without PT.Significantly lower β2-GPI levels(164.2±12 μg m L^-1 vs.234.2±16 μg mL^-1,P<0.001),higher anti-β2-GPI IgG levels(1.78±0.46 U mL^-1 vs.0.94±0.39 U mL^-1,P<0.001),and increased vWF activity(133.06%±30.50% vs.102.17%±25.90%,P<0.001) were observed in patients with PT than in those without PT.Both ADPinduced platelet aggregation(n=116,r^2=-0.5042,P<0.001) and vWF activity(n=116,r^2=-0.2872,P<0.001) were negatively correlated with β2-GPI levels.In summary,our data suggested that platelet aggregation and activation were significantly higher in patients with PT than in those without PT,which might be associated with reduced β2-GPI levels.The reduced β2-GPI levels might be due to the existence of anti-β2-GPI IgG.