Elevated platelet-associated IgG in PlA1-negative mothers following sensitization to the PlA1 antigen during pregnancy.

Between 1984 and 1990, we studied 25 infants with neonatal alloimmune thrombocytopenia caused by alloimmunization to the PlA1 alloantigen. We investigated whether mothers of these infants developed elevated platelet-associated immunoglobulin (PAIgG) in addition to anti-PlA1. Eight of the women were found to have PAIgG which persistent at least 7-10 days postdelivery. Eluates prepared from six of the women's platelets reacted with PlA1-positive and PlA1-negative donor platelets, and platelets from donors with Glanzmann's thrombasthenia. None of the women with elevated PAIgG had thrombocytopenia, eclampsia, or infections. Two women were found to have autoreactive antibodies present in plasma. These results indicate that elevated PAIgG may be found in women immunized to the PlA1 antigen. Some women may also have autoreactive antiplatelet antibodies in their plasma. These findings may lead to confusing serologic findings in evaluating the cause of neonatal alloimmune thrombocytopenia.