title: The avidity of anti-beta2-glycoprotein I antibodies in patients with or without antiphospholipid syndrome: a collaborative study in the frame of the European forum on antiphospholipid antibodies.
abstract: OBJECTIVE
  The objective of this study was to extend the findings of the preliminary study by measuring the avidity of IgG anti-β2-glycoprotein I antibodies (anti-β2-GPI) on a larger group of patients with primary or secondary antiphospholipid syndrome (APS) and anti-β2-GPI positive patients without APS in the frame of the European Forum on antiphospholipid antibodies (aPL).
  
  
  METHODS
  Serum from 137 patients with primary APS, APS associated with autoimmune diseases, and patients with autoimmune diseases other than APS from five EU rheumatology centres were tested for anti-β2-GPI antibodies. The 109 patients who were sera positive for anti-β2-GPI by the in-house anti-β2-GPI enzyme-linked immunosorbent assay (ELISA) at the Immunology Laboratory, UMC Ljubljana were selected for further testing on avidity with chaotropic anti-β2-GPI ELISA.
  
  
  RESULTS
  High, low and heterogeneous avidity IgG anti-β2-GPI was found in 32/109, 17/109 and 60/109 patients respectively. Significantly more patients with APS were in the high avidity than in the low avidity anti-β2-GPI group, while the opposite was observed for non-APS (both p < 0.001). The most common clinical feature among patients with high avidity anti-β2-GPI was thrombosis, mainly due to venous thrombosis (p < 0.01 and p < 0.001, versus low avidity anti-β2-GPI group).
  
  
  CONCLUSIONS
  Patients with or without APS had anti-β2-GPI of high, low or heterogeneous avidity. High avidity anti-β2-GPI was associated with thrombosis and APS, while in the low avidity anti-β2-GPI group non-APS (predominantly SLE) patients prevailed. Determination of anti-β2-GPI avidity should be considered in the analytical strategies for further differentiation of patients with anti-β2-GPI antibodies.
authors.affiliation: University Medical Centre, Department of Rheumatology, Ljubljana, Slovenia. sasa.cucnik@guest.arnes.si
authors.forename: S
authors.initials: S
authors.lastname: Cucnik
authors.forename: T
authors.initials: T
authors.lastname: Kveder
authors.forename: Z
authors.initials: Z
authors.lastname: Ulcova-Gallova
authors.forename: G Z
authors.initials: GZ
authors.lastname: Ulcova
authors.forename: J
authors.initials: J
authors.lastname: Swadzba
authors.forename: J
authors.initials: J
authors.lastname: Musial
authors.forename: G
authors.initials: G
authors.lastname: Valesini
authors.forename: T
authors.initials: T
authors.lastname: Avcin
authors.forename: B
authors.initials: B
authors.lastname: Rozman
authors.forename: B
authors.initials: B
authors.lastname: Bozic
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D017152:Antibodies, Antiphospholipid / Q000097:blood*; D000915:Antibody Affinity; D016736:Antiphospholipid Syndrome / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood*; D002648:Child; D005060:Europe; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D008297:Male; D008875:Middle Aged; D055815:Young Adult; D053482:beta 2-Glycoprotein I / Q000276:immunology*
chemical_list: D017152:Antibodies, Antiphospholipid; D001323:Autoantibodies; D007074:Immunoglobulin G; D053482:beta 2-Glycoprotein I