[Detection of antigenic determinants of autoantibodies in idiopathic thrombocytopenic purpura using anti-platelet monoclonal antibodies and flow cytometry in whole blood].

To detect antigenic sites of platelet-bound autoantibodies in chronic ITP, whole blood or platelet-rich plasma from patients was stained with monoclonal antibodies (MoAbs) directed against platelet membrane glycoproteins (GPs) and with FITC-conjugated anti-mice IgG in an unwashed system followed by flow cytometric analysis. Platelets were identified by light-scattering profile and the amount of anti GP MoAb bound to platelets was measured and expressed as mean fluorescence intensity. This system enabled to quantitate the amount of intact GPs on platelet surface, regardless of activation of platelet. As a result, decreased amount of platelet-bound anti GPIIb/IIIa MoAb was noted in 5 of 22 patients with chronic ITP comparing to those with normal subjects. On the contrary, none of these patients revealed any demonstrable decrease in the amount of anti GPIb MoAb binding. From these observations, we suggest that the decreased MoAb binding to platelets in these five patients indicates the binding of autoantibody directed toward antigenic determinants, which are on or close to the epitope of this MoAb.