Standardized measurement of major immunoglobulin class (IgG, IgA, and IgM) antibodies to β2glycoprotein I in patients with antiphospholipid syndrome

Abstract

Patients with the antiphospholipid syndrome (APS) have autoantibodies directed against epitopes on beta2 glycoprotein I (beta2GPI). We describe herein the performance characteristics of standardized enzyme-linked immunosorbent assays (ELISAs) for anti-beta2GPI of the three major immunoglobulin classes: IgG, IgA, and IgM. All three assays generated highly linear standard curves (5 points, r > or = 0.993 for each); precision was excellent both intra-assay and run-to-run, with coefficients of variation (CV) ranging from 2.3% to 6.6%. Values for IgG anti-beta2GPI correlated strongly with those obtained by an earlier method (r = 0.80, P< 0.0001). A study group consisting of 203 healthy subjects was used to generate percentile-based reference intervals for all three classes of anti-beta2GPI. APS subjects' anti-beta2GPI were found to differ significantly (P <0.0001 for each) from those of the control population. All three assays correlated well with beta2GPI-dependent anticardiolipin antibody (aCL) measurements; IgG: r = 0.94 (P <0.0001), for IgA: r = 0.82 (P<0.001) and for IgM: r = 0.84 (P<0.0001). We suggest that these ELISAs may provide valuable standardized measurements of IgG, IgA, and IgM anti-P2GPI.