Platelet-binding immunoglobulins in pregnancy-induced hypertension II. Origin of circulating IgG and IgM antiplatelet antibodies in the umbilical cord serum

Abstract

IgG and IgM have been identified on the surface of maternal platelets in both autoimmune thrombocytopenia (ATP) and pregnancy-induced hypertension (PIH). IgG is also found on the umbilical cord platelets of patients with ATP and PIH, whereas IgM is only found on the umbilical cord platelets of patients with PIH. The possible maternal or fetal origins of these umbilical cord blood immunoglobulins were investigated by immunoblot analysis of antibodies in paired maternal and umbilical cord blood sera of ATP and PIH patients. Maternal sera contained IgG and IgM antibodies which reacted with several platelet proteins, however, a large amount of patient-to-patient variation was observed in the specific antigens that were identified. Analysis of paired maternal and umbilical cord sera from patients with ATP or PIH showed identical patterns of antigen specificity, which suggested that the IgG antibodies in the fetal circulation were of maternal origin. Circulating IgM antibodies were not observed in the umbilical cord sera of ATP patients. The umbilical cord sera of PIH patients, however, contained IgM antibodies that reacted against a variety of platelet antigens. In addition, most umbilical cord sera from PIH patients had identical patterns and relative intensities of reactivity, which differed from the patterns observed in the paired maternal sera. Antiplatelet IgM in the umbilical cord blood of PIH patients, therefore, appears to be a product of the fetal immune system.