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[Anti-ß2 Glycoprotein I—ß2 Glycoprotein I] immune complexes in patients with antiphospholipid syndrome and other autoimmune diseases

P Rampazzo

T Brocco

F Barbero

Department of Clinical and Experimental Medicine, Thrombosis Center, University of Padova, Italy

A Rosato

Department of Oncology and Surgical Sciences, University of Padova, Italy

V Pengo

Department of Clinical and Experimental Medicine, Thrombosis Center, University of Padova, Italy; Department of Clinical and Experimental Medicine, Thrombosis Center, University of Padova School of Medicine, Ex Busonera' Hospital, via Gattamelata, 64 I 35128 Padova, Italy

Antiphospholipid syndrome (APS) is defined by the presence of aPL antibodies in patients with thromboembolic phenomena. Some antiphospholipid (aPL) antibodies, such as those directed against ß₂-glycoprotein I (ß₂GPI), are associated with thromboembolism, possess Lupus Anticoagulant (LA) activity and recognize their target antigen only when bound to specific surfaces or to phospholipids (PL). To ascertain whether both free and antibody-bound ß₂GPI circulate in APS, we set up an ELISA to detect [IgG anti-ß₂GPI–ß₂GPI] immune complexes. In this system, rabbit anti-human ß₂GPI antibodies were adsorbed onto plastic plates, incubated with patient plasma, and bound complexes were detected by means of alkaline phosphatase-labeled goat anti-human IgG; each assay was stopped when positive controls consisting of in vitro generated immune complexes reached an Optical Density (OD) of 0.5 at 405 nm. Plasma from 16 patients with APS showed a mean OD405 of 0.291 (range 0.115–0.558), not statistically different from the mean obtained for 15 age-and sex-matched healthy volunteers (mean OD405 = 0.169, range 0.066–0.264). Surprisingly, levels of immune complexes in 14 patients with other autoimmune diseases and no circulating anti-ß₂GPI antibodies were statistically higher (mean OD405 = 0.552, range 0.204–0.991) than those of healthy subjects and patients with APS. These data indicate that while autoantibodies to ß₂GPI are mainly unbound in plasma of patients with APS, they are complexed with their antigen in patients with other autoimmune diseases, possibly reflecting a higher binding affinity.

Key Words: anti-ß2-glycoprotein I • immune complexes • antiphospholipid syndrome

Lupus, Vol. 8, No. 2, 121-126 (1999)
DOI: 10.1191/096120399678847506


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