Discrepancy between antiplatelet antibody activities detected by immunoblot procedure and platelet counts in idiopathic thrombocytopenic purpura.

By immunoblot procedure it is possible to identify the pathogenic autoantibody responsible for platelet destruction in idiopathic thrombocytopenic purpura (ITP). We assessed the relationship between antiplatelet antibody activities detected by this technique and clinical thrombocytopenia in a patient with ITP whose antiplatelet autoantibody was directed toward an 85-kDa antigen. In this patient, over a 2-year-period, the platelet counts were not correlated with the levels of antiplatelet autoantibody detected by immunoblotting. The present observations suggest that IgG autoantibody directed toward a specific antigen is not necessarily a critical determinant of the degree of thrombocytopenia, and that factors other than IgG-Fc-receptor-mediated platelet destruction are also important in the determination of the disease activity in ITP.