Platelet autoantibody in a case of infectious mononucleosis presenting as thrombocytopenic purpura

In this unusual case acute thrombocytopenic purpura was the sole clinical manifestation of infectious mononucleosis. An antiplatelet antibody was demonstrated in the serum by two newly described technics: release of radioactive serotonin from platelets and inhibition of platelet aggregation following exposure of platelets to serum containing antiplatelet activity. The antiplatelet activity was completely inactivated by adsorption to washed platelets and was located in the immunoglobulin G (IgG) gamma globulin fraction of serum. The patient's serum also reacted against her own platelets indicating that the antiplatelet factor behaved as a true autoantibody.