FLOW CYTOMETRIC DETECTION OF CIRCULATING ACTIVATED PLATELETS IN PRIMARY ANTIPHOSPHOLIPID SYNDROME - CORRELATION WITH THROMBOCYTOPENIA AND ANTICARDIOLIPIN ANTIBODIES

Platelet activation has been suggested to play a crucial role in the p athogenesis of haemostatic disorders in antiphospholipid syndrome (APS ). In 16 patients with primary APS (PAPS) we investigated by flow cyto metry the presence of circulating activated platelets as defined by th e surface expression of activation-dependent glycoproteins CD62 and CD 63. In addition, the relationships among activated platelets, thromboc ytopenia, antiphospholipid antibodies (aPL) and platelet associated Ig G (PalgG) were evaluated. Compared to normal subjects CD62, but not CD 63 expression, was found significantly increased in patients. All thro mbocytopenic subjects showed a percentage of CD62 expressing platelets above the cut off. In thrombocytopenics a significantly increased per centage of CD62 and higher levels of aCL IgG were found compared to PA PS patients with normal platelet count. No correlation was found betwe en activated platelets and both lupus anticoagulant antibodies and Pal gG. Our data demonstrate that circulating activated platelets are dete ctable by flow cytometry in the majority of PAPS patients and suggest the existence of a relationship among activated platelets, thrombocyto penia and aPL levels.