In the
antiphospholipid syndrome (APS), patients produce
antiphospholipid antibodies (aPL) that promote
thrombosis and adverse pregnancy outcomes. Current
therapy with anticoagulation is only partially effective and associated with multiple complications. We previously discovered that aPL recognition of cell surface β2-glycoprotein I (β2-GPI) initiates
apolipoprotein E receptor 2 (apoER2)-dependent signaling in endothelial cells and in placental trophoblasts that ultimately promotes
thrombosis and fetal loss, respectively. Here we sought to identify a
monoclonal antibody (mAb) to β2-GPI that negates aPL-induced processes in cell culture and APS disease endpoints in mice. In a screen measuring endothelial
NO synthase (eNOS) activity in cultured endothelial cells, we found that whereas aPL inhibit eNOS, the mAb 1N11 does not, and instead 1N11 prevents aPL action. Coimmunoprecipitation studies revealed that 1N11 decreases pathogenic antibody binding to β2-GPI, and it blocks aPL-induced complex formation between β2-GPI and apoER2. 1N11 also prevents aPL antagonism of endothelial cell migration, and in mice it reverses the impairment in reendothelialization caused by aPL, which underlies the non-thrombotic vascular occlusion provoked by disease-causing
antibodies. In addition, aPL inhibition of trophoblast proliferation and migration is negated by 1N11, and the more than 6-fold increase in
fetal resorption caused by aPL in pregnant mice is prevented by 1N11. Furthermore, the promotion of
thrombosis by aPL is negated by 1N11. Thus, 1N11 has been identified as an mAb that attenuates APS-related
pregnancy complications and
thrombosis in mice. 1N11 may provide an efficacious, mechanism-based
therapy to combat the often devastating conditions suffered by APS patients.