Detection of anti-recombinant ββ2-glycoprotein 1 and anti-recombinant ββ2-glycoprotein 1 fifth-domain antibodies in sera from patients with systemic lupus erythematosus

Abstract

Two kinds of plasmid expression vectors which expressed β ₂-glycoprotein 1(β ₂GP1) and the fifth domain of β ₂-glycoprotein 1 (β ₂GP1-D5) were constructed respectively in this study. The antigenicity of recombinant β ₂GP1 (rβ ₂GP1) and β ₂GP1-D5 (rβ ₂GP1-D5) was identified by immunoblots using rabbit anti-β ₂GP1 antibodies, and the recombinant proteins were purified. Both anti-rβ ₂GP1 and anti-β ₂GP1-D5 antibodies in 112 patients were detected by ELISA using rβ ₂GP1 and rβ ₂GP1-D5 as coating antigens. A significant statistical correlation (r=0.667, P<0.01) between the levels of anti-β ₂GP1 and anticardiolipin (ACL) antibodies was found. The presence of anti-rβ ₂GP1 antibodies was associated with an increased frequency of history of thrombosis and/or recurrent abortion; hence anti-rβ ₂GP1 assay provided better specificity than conventional ACL assay. Detection of anti-rβ ₂GP1 antibodies may be of potential value in evaluating the risk of thrombosis and/or symptoms associated with other antiphospholipid syndromes (APS). The binding of anti-rβ ₂GP1 from the sera of patients with APS to rβ ₂GP1 was inhibited by rβ ₂GP1-D5. Meanwhile, of 28 patients who had positive anti-rβ ₂GP1 antibodies in sera, 27 (96.4%) had positive anti-rβ ₂GP1-D1 antibodies. This indicated that the antigenic epitope of β ₂GP1 may be located in its fifth domain.