A NEW PLATELET ALLOANTIGEN, TU(A), ON GLYCOPROTEIN-IIIA ASSOCIATED WITH NEONATAL ALLOIMMUNE THROMBOCYTOPENIA IN 2 FAMILIES

We describe immunization of two mothers against a new platelet alloantigen, designated Tu(a), in association with thrombocytopenia in their first born children. The platelet-specific antibodies were identified by a glycoprotein-specific platelet protein assay with husband's platelets. Monoclonal antibodies against glycoprotein complex IIb/IIIa (AP2) and against glycoprotein IIb (SZ22) could be used to immobilize the antigen bearing protein. When monoclonal antibodies against glycoprotein Ib/IX (FMC25) or Ia/IIa (Gi9) were used, no platelet-specific antibodies were detectable. The previously described alloantigens on the glycoprotein IIb/IIIa complex (HPA 1,3,4, Sr(a) and Va(a)) were not responsible for the reaction. Immunochemical analysis by an immunoblot assay showed that the Tu(a) antigen resides on GPIIIa but the antigen was destroyed by reduction of the protein. Altogether 10 individuals belonging to three unrelated families were shown to carry the antigen. The family studies within three generations indicated autosomal codominant inheritance. Thus the Tu(a) antigen is apparently different from all previously published platelet alloantigens. One Tu(a) positive blood donor was identified in a population study of approximately 150 individuals. This indicates a low frequency in the Finnish population. Extended population studies will be required to determine a more exact frequency of Tu(a) antigen.