HPA-1a antibodies are most commonly implicated in severe thrombocytopenia but HPA-5b and HPA-15b antibodies can also result in poor outcome. Postnatal transfusion management is extremely variable, and fetal transfusions are associated with significant morbidity and mortality.
Summary. The glycosylphosphatidylinositol-linked platelet protein CD109 carries the biallelic alloantigen system Gov. There is limited information on the incidence of Gov alloantibodies in neonatal alloimmune thrombocytopenia (NAITP), post-transfusion purpura (PTP) and platelet refractoriness. We adapted the monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay to the detection of Gov antibodies and determined their incidence in 605 archived samples (112 with HPA antibodies) referred for the aforementioned conditions. Here, we show that CD109 expression was reduced upon platelet storage in saline or by cryopreservation, but was stable when stored as whole blood or therapeutic platelet concentrate. Fourteen of the 605 samples contained Gov alloantibodies (anti-Gov a , n 10; anti-Gov b , n 4), with the majority in platelet refractoriness (n 9) and, of the remaining five, four in NAITP and one in PTP. In seven cases, no other HPA antibodies were detected, three being NAITP cases. The incidence of Gov antibodies was significantly lower than HPA-1 system antibodies (n 87), but equalled the number of HPA-5 system antibodies (n 14) and outnumbered HPA-2 and -3 system antibodies (10 altogether).
Neither severe thrombocytopenia nor ICH in HPA-1a-alloimmunized pregnancies can be predicted with sufficient sensitivity and specificity for clinical application from maternal anti-HPA-1a potency or bioactivity.
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