IgG and IgM antibodies to platelet membrane glycoprotein antigens in acute childhood idiopathic thrombocytopenic purpura

Abstract

In contrast to the situation in chronic idiopathic thrombocytopenic purpura (ITP) it has not been known whether acute childhood ITP has an autoimmune aetiology and to what extent autoantibodies directed to platelet autoantigens appear during the transient course of this disease. In the present study of 21 children with acute ITP an immunoblot technique was applied to detect serum antibodies to electrophoretically (SDS-PAGE) separated normal donor platelet membrane proteins. Platelet antigen binding antibodies detected by alkaline phosphatase conjugated protein A or anti-IgM antibody were observed in 13 out of 21 (62%) patients while controls were negative. In nine children antibodies were directed to antigens localized on the three major membrane glycoproteins. GPIb (four), GPIIb (one) and GPIIIa (five). Antibodies to a 250 kDa antigen were noted in one case and to smaller 25-52 kDa proteins in 12 patients. Four patients had IgG as well as IgM platelet antibodies while in nine only IgM was found. The reactions were eliminated after absorptions of sera with fresh platelets. In all of three tested patients the glycoprotein antigen specific antibodies could be detected in acid eluates prepared from the absorbing platelets. The presence of antibodies, predominantly IgM, to platelet surface antigens in a majority of the children with acute ITP, may suggest an autoimmune process, albeit transitory, similar to that in chronic ITP.