Influences of antiplatelet autoantibodies on platelet function in immune thrombocytopenic purpura

We investigated the characteristics of the antiplatelet autoantibodies in 60 patients with ITP. Using flow cytometry, the binding of monoclonal antibodies to the platelet glycoprotein (GP) IIb/IIIa complex and to GPIb was examined in these patients. The extent of binding was decreased in 15 patients (anti-GPIIb/IIIa in 12 patients and both anti-GPIIb/IIIa and anti-GPIb in 3 patients). Western blotting revealed that 10 of these 15 patients had either anti-GPIIb or anti-GPIIIa and 2 had anti-GPIb autoantibodies. ADP-induced aggregation of normal platelets was inhibited by autoantibodies in 12 of 60 patients, and 11 of these had anti-GPIIb/IIIa antibodies. Ristocetin-induced aggregation was inhibited in 4 of these patients, and 2 with prominent inhibition had anti-GPIb antibodies. There was a significant relationship between platelet-associated IgG value and ATP secretion. These results suggest that some antiplatelet autoantibodies can affect platelet function and thus have an influence on the pathophysiology of ITP.