International standards for IgG and IgM anti-β2glycoprotein antibody measurement

Abstract

International standards for anti-beta2 glycoprotein I (anti-β₂GPI) testing are needed. We evaluated the suitability of polyclonal/monoclonal candidate reference materials (RM) for the assay. IgG/IgM anti-β₂GPI were affinity-purified (AP) from high-positive antiphospholipid syndrome sera and IgG from HCAL clone supernatant. Igs were tested for purity by SDS-PAGE, pooled, concentrated, sterile-filtered and the protein concentration determined. One unit was defined as the binding activity of 1 µg/ml of AP anti-β₂GPI Ig. IgG/IgM RM were each assigned a unit value using the respective AP material as a calibrator. Polyclonal/monoclonal RM and 30 samples were evaluated for linearity, unit equivalency and commutability. Polyclonal AP material was assigned a value of 100 U IgG and 15 U IgM anti-β₂GPI, respectively. IgG-RM had a value of 270 IgG and the IgM-RM of 220.3 IgM anti-β₂GPI U. The linearity (R²) of each RM curve for the various assays ranged from 0.96 to 0.99. Commutability samples fit very well within 95% prediction intervals and had excellent correlation when comparing assays. IgG and IgM polyclonal and IgG monoclonal RM displayed excellent linearity and commutability, being good candidates for better standardization of anti-β₂GPI immunoassays.

Keywords

reference materials standardization

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References

Miyakis

Lockshin

Atsumi

. International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS). J Thromb Haemost 2006; 4: 295–306.

Meroni

Borghi

Raschi

Tedesco

. Pathogenesis of antiphospholipid syndrome: Understanding the antibodies. Nat Rev Rheumatol 2011; 7: 330–339.

Meroni

Biggioggero

Pierangeli

Sheldon

Zegers

Borghi

. Standardization of autoantibody testing: A paradigm for serology in rheumatic diseases. Nat Rev Rheumatol 2014; 10: 35–43.

Meroni PL, Chighizola CB, Rovelli F, Gerosa M. Antiphospholipid syndrome in 2014: More clinical manifestations, novel pathogenic players and 2 emerging biomarkers. Arth Res Ther 2014 [in press].

de Laat

Derksen

Urbanus

de Groot

. IgG antibodies that recognize epitope Gly40-Arg43 in domain I of beta 2-glycoprotein I cause LAC, and their presence correlates strongly with thrombosis. Blood 2005; 105: 1540–1545.

Pengo

Banzato

Denas

. Correct laboratory approach to APS diagnosis and monitoring. Autoimmun Rev 2013; 12: 832–834.

Reber

Tincani

Sanmarco

de Moerloose

Boffa

. European Forum on Antiphospholipid Antibodies Standardization Group. Variability of anti-beta2 glycoprotein I antibodies measurement by commercial assays. Thromb Haemost 2005; 94: 665–672.

Pierangeli

Favaloro

Lakos

. Standards and reference materials for the anticardiolipin and anti-β(2)glycoprotein I assays: A report of recommendations from the APL Task Force at the 13th International Congress on Antiphospholipid Antibodies. Clin Chim Acta 2012; 413: 358–360.

Lakos

Favaloro

Harris

. International consensus guidelines on anticardiolipin and anti-β(2) glycoprotein I testing: A report from the APL Task Force at the 13th International Congress on Antiphospholipid Antibodies. Arthritis Rheum 2012; 64: 1–10.

10.

Tincani

Spatola

Prati

. The antibeta2-glycoprotein I activity in human anti-phospholipid syndrome sera is due to monoreactive low-affinity autoantibodies directed to epitopes located on native beta2-glycoprotein I and preserved during species’ evolution. J Immunol 1996; 157: 5732–5738.