Idiopathic (autoimmune) thrombocytopenic purpura with a complement-fixing autoantibody and response to plasma exchange.

A 69-year-old male presented with severe, life-threatening thrombocytopenia, subsequently diagnosed as autoimmune thrombocytopenic purpura (ATP). A potent complement-activating platelet-specific autoantibody was present in the patient's serum. The IgG autoantibody induced lysis of autologous and isologous platelets but was nonreactive with red cells and lymphocytes. It reacted in an indirect immunofluorescence test with platelets from 50 control subjects and with thrombasthenic platelets but failed to react with platelets from a patient with the Bernard-Soulier syndrome (BSS), suggesting that it recognizes a glycoprotein absent from BSS platelets. Treatment by exchange transfusion and plasmapheresis was followed by disappearance of the autoantibody and sustained remission.