Nature of platelet antibody in Evans syndrome: a case report

The association of autoimmune thrombocytopenia and autoimmune hemolytic anemia (Evans Syndrome) has been recognized previously. Recently the present authors investigated a patient with this disorder. Both IgG and C3d were found on the patient's red cells and the serum contained a polyspecific IgG red cell antibody demonstrable only by the antiglobulin test. IgG antiplatelet antibody was demonstrated on circulating platelets as well as in the serum from the patient by using 125I-staphylococcal Protein A (ISPA) assay. Absorption of serum with normal platelets resulted in removal of platelet antibody, but not the red cell antibody. Furthermore, eluate prepared from platelets sensitized with patient serum contained an IgG antibody directed specifically against platelets, since it did not cross react with red cells. Our data suggest the presence of two distinct antibodies, one directed against platelets and the other against red cells in our patient with Evans Syndrome. Both these antibodies are IgG in nature and belong to subclass other than IgG3 since staphylococcal Protein A (SPA) binds to all subclasses of human IgG except IgG3.