A CASE OF NEONATAL ALLOIMMUNE THROMBOCYTOPENIA IN THE PRESENCE OF THREE DIFFERENT anti-HPA ANTIBODIES: HPA-4b, HPA-5a, AND HPA-15b ANTIBODIES

Abstract

Neonatal alloimmune thrombocytopenia (NAIT) is caused by the formation of maternal alloantibodies against fetal platelet antigens. Multiple anti- human platelet antigen (HPA) alloantibodies have occasionally been detected in maternal sera. In this case report, we present the first Japanese NAIT case with three different anti-HPA antibodies. The proband (second sibling) showed mild thrombocytopenia (73 × 10³/μl) without any bleeding tendency at birth. Human leukocyte antigen (HLA) antibodies were negative. A screening assay employing the mixed-passive hemagglutination (MPHA) method suggested the presence of multiple anti-HPA antibodies including anti-HPA-5a antibodies. A monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay demonstrated a reaction between maternal antibodies and paternal platelets and suggested the presence of alloantibodies against HPA-4, HPA-5, HPA-6, and HPA-15. We also determined the maternal, paternal, and proband's HPA genotype. Furthermore, a MAIPA assay using K562 cells expressing each HPA confirmed the presence of three different alloantibodies, HPA-4b, HPA-5a, and HPA-15b antibodies, in maternal serum. This case strongly suggests that the combined use of MPHA and MAIPA assays may be powerful for detecting and identifying multiple alloantibodies.