title: Prevalence and clinical significance of low-avidity HPA-1a antibodies in women exposed to HPA-1a during pregnancy.
abstract: BACKGROUND
  Recent studies suggest that HPA-1a-specific, low-avidity maternal antibodies not detectable by conventional methods can cause neonatal alloimmune thrombocytopenia (NAIT). We performed studies to further define the incidence and clinical significance of this type of antibody.
  
  
  METHODS
  Surface plasmon resonance analysis was used to detect low-avidity antibodies in HPA-1a-negative, "antibody-negative" mothers of suspected NAIT cases. The ability of antibodies detected to promote immune destruction of human platelets (PLTs) was examined in a newly developed NOD/SCID mouse model.
  
  
  RESULTS
  Among 3478 suspected cases of NAIT, 677 HPA-1a-negative mothers were identified. HPA-1a-specific antibodies were detected by conventional antibody testing in 616 cases (91%). Low-avidity HPA-1a-specific antibodies were identified in 18 of the remaining 61 cases (9%). Clinical follow-up on 13 cases showed that eight were referred because of suspected NAIT and five because the mother's sister had previously had an infant with NAIT. Only six infants born to the 13 sensitized mothers had clinically significant thrombocytopenia at birth. Three of four low-avidity antibodies tested in the mouse caused accelerated clearance of HPA-1a/a but not HPA-1b/b PLTs. Only 3 of 12 mothers with low-avidity HPA-1a antibodies were positive for HLA-DRB3*0101.
  
  
  CONCLUSIONS
  The findings confirm previous reports that low-avidity HPA-1a antibodies can cause NAIT but show that the presence of such an antibody does not predict that an infant will be affected. The low incidence of HLA-DRB3*0101 in this cohort (p < 0.0001) suggests that women negative for DRB3*0101 may be predisposed to produce low-avidity HPA-1a antibodies.
authors.affiliation: Blood Research Institute and Platelet & Neutrophil Immunology Laboratory, BloodCenter of Wisconsin, Milwaukee,WI 53226-3548, USA. Julie.Peterson@bcw.edu
authors.forename: Julie A
authors.initials: JA
authors.lastname: Peterson
authors.forename: Adam
authors.initials: A
authors.lastname: Kanack
authors.forename: Dhirendra
authors.initials: D
authors.lastname: Nayak
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Bougie
authors.forename: Janice G
authors.initials: JG
authors.lastname: McFarland
authors.forename: Brian R
authors.initials: BR
authors.lastname: Curtis
authors.forename: Richard H
authors.initials: RH
authors.lastname: Aster
mesh_terms: D000818:Animals; D000915:Antibody Affinity / Q000276:immunology; D016824:Antigens, Human Platelet / Q000276:immunology*; D001792:Blood Platelets / Q000276:immunology; D015331:Cohort Studies; D005260:Female; D059826:HLA-DRB3 Chains / Q000276:immunology; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D039661:Integrin beta3; D008297:Male; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology* / Q000276:immunology*; D015995:Prevalence; D016036:Seroepidemiologic Studies; D020349:Surface Plasmon Resonance; D054098:Thrombocytopenia, Neonatal Alloimmune / Q000453:epidemiology* / Q000276:immunology*
chemical_list: D016824:Antigens, Human Platelet; D059826:HLA-DRB3 Chains; C061248:ITGB3 protein, human; D039661:Integrin beta3