The association of thrombosis and gestational morbidity with antiphospholipid antibodies is termed antiphospholipid syndrome (APS). Annexin 2 (A2) is a profibrinolytic endothelial cell surface receptor that binds plasminogen, its tissue activator (tPA), and beta(2)-glycoprotein I (beta2GPI), the main antigen for antiphospholipid antibodies. Here, we evaluate A2 as a target antigen in APS. Serum samples from 434 individuals (206 patients with systemic lupus erythematosus without thrombosis, 62 with APS, 21 with nonautoimmune thrombosis, and 145 healthy individuals) were analyzed by enzyme-linked immunosorbent assay (ELISA) and immunoblot for antiphospholipid and A2 antibodies. Anti-A2 antibodies (titer > 3 SDs) were significantly more prevalent in patients with APS (22.6%; venous, 17.5%; arterial, 34.3%; and mixed thrombosis, 40.4%) than in healthy individuals (2.1%, P < .001), patients with nonautoimmune thrombosis (0%, P = .017), or patients with lupus without thrombosis (6.3%, P < .001). Anti-A2 IgG enhanced the expression of tissue factor on endothelial cells (6.4-fold +/- 0.13-fold SE), blocked A2-supported plasmin generation in a tPA-dependent generation assay (19%-71%) independently of beta2GPI, and inhibited cell surface plasmin generation on human umbilical vein endothelial cells (HUVECs) by 34% to 83%. We propose that anti-A2 antibodies contribute to the prothrombotic diathesis in antiphospholipid syndrome.

The association of thrombosis, obstetric morbidity, and hemocytopenias with antiphospholipid antibodies is termed antiphospholipid syndrome. Annexin 2 is a profibrinolytic endothelial cell surface receptor that binds plasminogen, its tissue activator (tPA), and beta-2-glycoprotein-I, the main antigen for antiphospholipid antibodies. Here we evaluate annexin 2 as a target antigen in antiphospholipid syndrome. Serum samples from 434 individuals (206 patients with systemic lupus erythematosus without thrombosis, 62 with antiphospholipid syndrome, 21 with non-autoimmune thrombosis, and 145 healthy individuals) were analyzed by ELISA and immunoblotting for antiphospholipid and annexin 2 antibodies. IgG was purified and the effect of anti-annexin 2 antibodies on human umbilical vein endothelial cell activation and cell surface plasmin generation were evaluated. Anti-annexin 2 antibodies (titer &gt;3SD) were significantly more prevalent in patients with antiphospholipid syndrome (22.6%, venous 17.5%, arterial 34.3% and mixed thrombosis 40.4%), than in healthy individuals (2.1%, p&lt;0.001), patients with non-autoimmune thrombosis (0%, p=0.017) or patients with lupus without thrombosis (6.3%, p&lt;0.001). Anti-annexin 2 antibodies enhanced the expression of tissue factor, a procoagulant protein, on endothelial cells (6.4 fold ± 0.13 SE), and blocked the fibrinolytic cofactor activity of purified placental annexin 2 in a tissue plasminogen activator-dependent plasmin generation assay (19 – 71%), independently of beta-2-glycoprotein-I. Similarly, cell surface plasmin generation on human umbilical vein endothelial cells was inhibited by 34–83%. We conclude that antibodies against the fibrinolytic receptor annexin 2 are significantly associated with thrombosis in antiphospholipid syndrome, and that anti-annexin 2 antibodies activate endothelial cells and inhibit endothelial cell surface-localized plasmin generation. We propose that these mechanisms contribute to the prothrombotic tendency in antiphospholipid syndrome.

Available evidence indicates that many women with SLE can be considered good candidates for most contraceptive methods, including hormonal contraceptives. The benefits of contraception for many women with SLE likely outweigh the risks of unintended pregnancy in this population. Women with positive antiphospholipid antibodies are not good candidates for combined hormonal contraception given their elevated baseline risk of thrombosis.

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