ABSTRACT
Beta 2 glycoprotein I (apolipoprotein H, beta 2GPI) is involved in the formation of epitope(s) recognized by clinically relevant autoantibodies from patients with antiphospholipid syndrome. We studied the binding of beta 2GPI to chemically activated polystyrene in a microtitre plate format. Adsorption isotherms (at 37 degrees C) were generated for beta 2GPI on activated polystyrene and on unactivated polystyrene, with both human serum antibodies and rabbit polyclonal IgG antibodies as probes, and horseradish peroxidase (HRP)-tagged anti-IgG to detect binding. Additionally, beta 2GPI was biotinylated and isotherms were developed by using HRP-streptavidin as the recognition sequence. Human serum autoantibodies, which did not precipitate beta 2GPI in solution, yielded a characteristic chemisorption isotherm on activated polystyrene but did not recognize beta 2GPI bound to untreated polystyrene. The rabbit IgG, which did precipitate beta 2GPI in solution, detected beta 2GPI bound to both activated polystyrene and, to a lesser extent, to untreated polystyrene. The binding of beta 2GPI to untreated polystyrene was confirmed by the use of biotinylated beta 2GPI. To assess the prevalence of IgG anti-beta 2GPI autoantibodies, we surveyed 113 sera submitted to our laboratory for anticardiolipin antibody (aCL) testing. Only nine (8%) had anti-beta 2GPI activity greater than two standard deviations above the mean for those sera in which aCL activity was within normal limits. We conclude that epitope presentation of beta 2GPI for human autoantibody binding is dependent on surface properties of the polystyrene, and that beta 2GPI autoantibodies are found only in a subpopulation of sera positive for aCL.
Subject(s)
Apolipoproteins/metabolism , Autoantibodies/metabolism , Glycoproteins/metabolism , Immunoglobulin G/metabolism , Polystyrenes/metabolism , Adsorption , Animals , Autoantibodies/immunology , Bacterial Proteins/chemistry , Binding Sites , Enzyme-Linked Immunosorbent Assay , Horseradish Peroxidase/chemistry , Humans , Immunoglobulin G/immunology , Pilot Projects , Rabbits , Reference Standards , Streptavidin , beta 2-Glycoprotein IABSTRACT
OBJECTIVE: To examine IgG anti-beta 2 glycoprotein I (anti-beta 2 GPI) binding in 82 sera referred for anticardiolipin antibody (aCL) testing and to develop preliminary clinical correlations with antiphospholipid syndrome (APS). METHODS: Immunoassay of IgG cofactor dependent aCL and IgG anti-beta 2 GPI antibodies and retrospective chart review. RESULTS: Forty-four sera exhibited normal (< or = 22 GPL units) aCL activity, 18 had moderate binding activity (23-45 GPL units), and 20 had high (> or = 46 GPL units) binding activity to cardiolipin. Among these groups, 6 of the 20 sera in the high GPL group had elevated anti-beta 2 GPI. This correlated strongly with 2 or more clinical manifestations of APS. CONCLUSION: Anti-beta 2 GPI activity may be a more valuable indicator of APS than aCL.
