Novel Assays of Thrombogenic Pathogenicity in the Antiphospholipid Syndrome Based on the Detection of Molecular Oxidative Modification of the Major Autoantigen β2-Glycoprotein I

Objective. Beta-2-glycoprotein I (beta(2)GPI) constitutes the major autoantigen in the antiphospholipid syndrome (APS), a common acquired cause of arterial and venous thrombosis. We recently described the novel observation that beta(2)GPI may exist in healthy individuals in a free thiol (biochemically reduced) form. The present study was undertaken to quantify the levels of total, reduced, and posttranslationally modified oxidized beta(2)GPI in APS patients compared to various control groups.Methods. In a retrospective multicenter analysis, the proportion of beta(2)GPI with free thiols in serum from healthy volunteers was quantified. Assays for measurement of reduced as well as total circulating beta(2)GPI were developed and tested in the following groups: APS (with thrombosis) (n = 139), autoimmune disease with or without persistent antiphospholipid antibodies (aPL) but without APS (n = 188), vascular thrombosis without APS or aPL (n = 38), and healthy volunteers (n = 91).Results. Total beta(2)GPI was significantly elevated in patients with APS (median 216.2 mu g/ml [interquartile range 173.3-263.8]) as compared to healthy subjects (median 178.4 mu g/ml [interquartile range 149.4-227.5] [P < 0.0002]) or control patients with autoimmune disease or vascular thrombosis (both P < 0.0001). The proportion of total beta(2)GPI in an oxidized form (i.e., lacking free thiols) was significantly greater in the APS group than in each of the 3 control groups (all P < 0.0001).Conclusion. This large retrospective multicenter study shows that posttranslational modification of beta(2)GPI via thiol-exchange reactions is a highly specific phenomenon in the setting of APS thrombosis. Quantification of posttranslational modifications of beta(2)GPI in conjunction with standard laboratory tests for APS may offer the potential to more accurately predict the risk of occurrence of a thrombotic event in the setting of APS

Posttranslational forms of beta 2-glycoprotein I in the pathogenesis of the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an autoimmune disease characterised by a procoagulant state that predisposes to recurrent thrombosis and miscarriages. Two major discoveries have advanced our understanding of the underlying complex pathogenesis of the APS. The first was the discovery that beta-2 glycoprotein-1 (β2GPI) is the major auto antigen in APS. The second was the discovery in more recent years that β2GPI contains allosteric disulphide bonds susceptible to posttranslational modification that may be involved in the development of autoantibodies in APS. The main allosteric disulphide bond in the fifth domain of β2GPI can exist in two redox states: free thiol or oxidised. It is the conformational transformation of β2GPI from its free thiol form to its more immunogenic oxidised form that exposes neo-epitopes on the first and fifth domains. The purpose of this review is to highlight the recent findings on the posttranslational forms of β2GPI in the pathogenesis of APS. We suggest that novel assays quantitating the different redox forms of β2GPI in plasma or serum may be used to supplement existing clinical and laboratory assays to more accurately stratify risk of thrombosis or miscarriage in APS patients