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FRI0563 Detection of IGG Anti-Domain I Beta2 Glycoprotein I Antibodies by Chemiluminescence Immunoassay in Primary Antiphospholipid Syndrome
  1. L. Meneghel1,
  2. A. Ruffatti1,
  3. S. Gavasso2,
  4. M. Tonello1,
  5. E. Mattia1,
  6. L. Spiezia2,
  7. D. Tormene2,
  8. A. Hoxha1,
  9. M. Fedrigo3,
  10. P. Simioni2
  1. 1Rheumatology Unit, Department of Medicine
  2. 2Chair of Internal Medicine, Department of Medicine
  3. 3Chair of Cardiovascular Pathology, Department of Cardiological, Thoracic and Vascular Sciences, Università di Padova, Padova, Italy

Abstract

Background IgG anti-Domain I (anti-DI) β2 Glycoprotein I (β2GPI) antibodies are the main subset of anti-β2GPI antibodies and are associated to thrombotic risk in antiphospholipid syndrome (APS), but their detection is technically difficult because the Domain I (DI) epitope is exposed only upon a conformational change in β2GPI molecule. Chemiluminescence immunoassay (CLIA), a new fully-automated technology which exploits a light-emitting chemical reaction for antibody detection, has become available for testing anticardiolipin (aCL) and anti-β2GPI antibodies and, recently, also anti-DI antibodies.

Objectives The aim of this study was to assess the clinical value of IgG anti-DI antibodies in a large homogeneous cohort of primary APS patients and in a group of ELISA-negative patients with clinical manifestations of APS.

Methods The study population included 88 patients with PAPS, 63 ELISA-negative subjects and 96 controls. IgG anti-DI, IgG anticardiolipin (aCL), IgG anti-β2GPI antibodies were assayed using CLIA (HemosIL AcuStar®). Lupus Anticoagulant (LA) was assessed according to the updates international guidelines [1].

Results The sensitivity and specificity of IgG anti-DI antibodies were comparable to those of IgG aCL and IgG anti-β2GPI antibodies, while IgG anti-DI antibody sensitivity was significantly higher than that of LA (Table 1). There was a significant agreement and association (p<0.001 for both) and a significant titre correlation (p<0.001) between IgG anti-DI and IgG aCL as well as IgG anti-β2GPI antibodies (Table 2). IgG anti-DI antibody prevalence and mean titres were significantly higher in the thrombotic than in the pregnancy morbidity PAPS patients (79.6% vs 23.5% and 823.9 CU vs 34.0 CU, p<0.001 for both). Among the conventional aPL antibody profiles, the frequency of IgG anti-DI antibodies and their titres were significantly higher in the triple positivity group (94.1%, 1162.5 CU) compared to single (15.0%, 4.1 CU) and double positivity (47.1%, 443.8 CU) ones (p<0.001 for both). Finally, the prevalence of IgG anti-DI antibodies detected by the CLIA method was not significantly different in the ELISA-negative patients compared to that found in the controls (6.3% vs 3.7%, p=0.47).

Table 1

Table 2

Conclusions This study provides further evidence that anti-DI antibodies can be considered a promising biomarker for both APS classification and risk assessment particularly in patients suffering from vascular thrombosis.

References

  1. Pengo V, Tripodi A, Reber G, Rand JH, Ortel TL, Galli M et al. Update of the guidelines for lupus anticoagulant detection. Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibody of the Scientific and Standardisation Committee of the International Society on Thrombosis and Haemostasis. J Thromb Haemost 2009;7:1737-40.

Disclosure of Interest None declared

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