title: Low-avidity anti-HPA-1a alloantibodies are capable of antigen-positive platelet destruction in the NOD/SCID mouse model of alloimmune thrombocytopenia.
abstract: 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.
  
  
  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.
authors.affiliation: Institute for Clinical Immunology and Transfusion Medicine, Medical Faculty, Justus Liebig University Giessen, Giessen, Germany.
authors.forename: Tamam
authors.initials: T
authors.lastname: Bakchoul
authors.forename: Sebastian
authors.initials: S
authors.lastname: Kubiak
authors.forename: Annika
authors.initials: A
authors.lastname: Krautwurst
authors.forename: Monika
authors.initials: M
authors.lastname: Roderfeld
authors.forename: Hans C
authors.initials: HC
authors.lastname: Siebert
authors.forename: Gregor
authors.initials: G
authors.lastname: Bein
authors.forename: Ulrich J
authors.initials: UJ
authors.lastname: Sachs
authors.forename: Sentot
authors.initials: S
authors.lastname: Santoso
mesh_terms: D000818:Animals; D000915:Antibody Affinity; D016824:Antigens, Human Platelet / Q000276:immunology*; D001792:Blood Platelets / Q000276:immunology*; D015331:Cohort Studies; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D039661:Integrin beta3; D007518:Isoantibodies / Q000276:immunology*; D008297:Male; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D012189:Retrospective Studies; D054098:Thrombocytopenia, Neonatal Alloimmune / Q000276:immunology*
chemical_list: D016824:Antigens, Human Platelet; C061248:ITGB3 protein, human; D039661:Integrin beta3; D007518:Isoantibodies