ANTIPLATELET GLYCOPROTEIN AUTOANTIBODIES IN PATIENTS WITH AUTOIMMUNE-DISEASES WITH AND WITHOUT THROMBOCYTOPENIA

The presence and specificity of antiplatelet autoantibodies in 32 pati ents with primary and 18 patients with secondary autoimmune thrombocyt openic purpura (AITP), as well as 11 nonthrombocytopenic patients with systemic autoimmune diseases, were studied. By means of the direct an d indirect monoclonal antibody immobilization of platelet antigen (MAI PA) assay, antiplatelet autoantibodies were detected using monoclonal antibodies specific for platelet glycoproteins (GPs) Ib, IIb/IIIa, Ia/ IIa, and IV. Serum antiplatelet autoantibodies were found in 18 of 32 primary AITP patients (56%), 6 of 28 secondary AITP patients (33%), an d 5 of 11 nonthrombocytopenic patients (45%). Platelet-associated auto antibodies were detected in five of eight patients with primary (62%) and in four of eight patients with secondary AITP (50%) and in two of four patients without thrombocytopenia (50%). Multiple antibody reacti vity, mainly against GPs IIb/IIIa and Ib and, in a few patients, again st Ia/IIa, was found. Using MAIPA, platelet xylene eluates from 20 pat ients were also studied. Antiplatelet elutable autoantibodies were rel ated to thrombocytopenia; autoantibodies against membrane GPs Ib and I Ib/IIla were demonstrable in 84 and 63% of eluates from patients with primary and secondary AITP, respectively but not in eluates from nonth rombocytopenic patients. The presence of antiplatelet antibodies thus appears to be a common feature of many autoimmune diseases apart from the thrombocytopenia, but the (primary or secondary) etiology of the i mmune thrombocytopenia cannot be differentiated on the grounds of thei r specificity.