Low-avidity anti-HPA-1a alloantibodies are capable of antigen-positive platelet destruction in the NOD/SCID mouse model of alloimmune thrombocytopenia

• Published in: Transfusion (Philadelphia, Pa.) Pa.), 2011-11, Vol.51 (11), p.2455-2461
• Main Authors: Bakchoul, Tamam, Kubiak, Sebastian, Krautwurst, Annika, Roderfeld, Monika, Siebert, Hans C., Bein, Gregor, Sachs, Ulrich J., Santoso, Sentot
• Format: Article
• Language: English
• Subjects: Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Animals; Antibody Affinity; Antigens, Human Platelet - immunology; Biological and medical sciences; Blood Platelets - immunology; Blood. Blood and plasma substitutes. Blood products. Blood cells. Blood typing. Plasmapheresis. Apheresis; Blood. Blood coagulation. Reticuloendothelial system; Cohort Studies; Disease Models, Animal; Female; Humans; Infant, Newborn; Isoantibodies - immunology; Male; Medical sciences; Mice; Mice, Inbred NOD; Mice, SCID; Pharmacology. Drug treatments; Retrospective Studies; Thrombocytopenia, Neonatal Alloimmune - immunology; Transfusions. Complications. Transfusion reactions. Cell and gene therapy
• ISSN: 0041-1132; 1537-2995
• DOI: 10.1111/j.1537-2995.2011.03171.x

BACKGROUND: Neonatal alloimmune thrombocytopenia (NAIT) is mostly caused by maternal antibodies against human platelet antigen 1a (HPA‐1a) expressed on glycoprotein (GP) IIb/IIIa. Accumulated evidence indicated that anti‐HPA‐1a could be overlooked by standard methods due to low avidity. Low‐avidity HPA‐1a antibodies were shown to be detectable by surface plasmon resonance (SPR). We sought to investigate the frequency and in vivo relevance of low‐avidity anti‐HPA‐1a. STUDY DESIGN AND METHODS: A retrospective cohort consisting of 82 HPA‐1bb mothers of HPA‐1ab newborns with thrombocytopenia was analyzed using standard serologic methods. Maternal immunoglobulin (Ig)G fractions were investigated for low‐avidity antibodies in SPR using purified GPIIb/IIIa (HPA‐1a or ‐1b). The capability of HPA‐1a antibodies to clear platelets (PLTs) in vivo was analyzed using the NOD/SCID mouse model of alloimmune thrombocytopenia. RESULTS: HPA antibodies were detectable in sera from 68 of 82 (83%) mothers using standard serologic methods and undetectable in 14 of 82 sera. In SPR, IgG fractions of sera reacting positive in monoclonal antibody immobilization of PLT antigen (MAIPA) assay showed specific binding to an HPA‐1a flow cell (mean, 87 ± 21 resonance units [RU]). When MAIPA‐negative sera were tested in SPR, binding with low avidity was observed in 7 of 14 to HPA‐1a (mean, 31 ± 5 RU), but not to HPA‐1b flow cell (mean, 5 ± 2 RU). In vivo, low‐avidity antibodies were capable of clearing HPA‐1ab PLTs but not HPA‐1bb PLTs in a NOD/SCID mouse model. Elimination kinetics were slower than observed with MAIPA‐positive antibodies. CONCLUSIONS: Low‐avidity HPA‐1a antibodies are present in a significant number of NAIT cases and, although they can escape detection by standard serology, they harbor the capability of PLT destruction in vivo.