Detection of anti-recombinant ββ2-glycoprotein 1 and anti-recombinant ββ2-glycoprotein 1 fifth-domain antibodies in sera from patients with systemic lupus erythematosus
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Two kinds of plasmid expression vectors which expressed β2-glycoprotein 1(β2GP1) and the fifth domain of β2-glycoprotein 1 (β2GP1-D5) were constructed respectively in this study. The antigenicity of recombinant β2GP1 (rβ2GP1) and β2GP1-D5 (rβ2GP1-D5) was identified by immunoblots using rabbit anti-β2GP1 antibodies, and the recombinant proteins were purified. Both anti-rβ2GP1 and anti-β2GP1-D5 antibodies in 112 patients were detected by ELISA using rβ2GP1 and rβ2GP1-D5 as coating antigens. A significant statistical correlation (r=0.667, P<0.01) between the levels of anti-β2GP1 and anticardiolipin (ACL) antibodies was found. The presence of anti-rβ2GP1 antibodies was associated with an increased frequency of history of thrombosis and/or recurrent abortion; hence anti-rβ2GP1 assay provided better specificity than conventional ACL assay. Detection of anti-rβ2GP1 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-rβ2GP1 from the sera of patients with APS to rβ2GP1 was inhibited by rβ2GP1-D5. Meanwhile, of 28 patients who had positive anti-rβ2GP1 antibodies in sera, 27 (96.4%) had positive anti-rβ2GP1-D1 antibodies. This indicated that the antigenic epitope of β2GP1 may be located in its fifth domain.
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