[Sr(a), a "private" thrombocyte alloantigen as a cause of neonatal alloimmune thrombocytopenia]

Neonatal alloimmune thrombocytopenia (NAIT) is caused by maternal immunization against fetal platelet antigens. In the serum of a mother who gave birth to a child with the typical clinical picture of NAIT we found an antibody directed against the new platelet antigen Sra. Anti-Sra was found to react in the immunofluorescence test and in a glycoprotein (GP) specific immunoassay (MAIPA) using a monoclonal antibody against GP IIb/IIIa for antigen immobilization with the child's and father's platelets. Radioimmunoprecipitation and immunoblot allowed to assign the Sra-antigen to GP IIIa. The phenotype frequency was estimated less than 1%, characterising the Sra-antigen as the first 'private' alloantigen on platelets.