Abstract 12956: Monoclonal Antibody to Domain I of β2-glycoprotein I Prevents the Thrombotic Diathesis Associated With the Antiphospholipid Syndrome
Patients with antiphospholipid syndrome (APS) have exaggerated thrombosis caused by antiphospholipid antibodies (aPL). Current therapy with anticoagulation is sometimes ineffective and can lead to bleeding complications. We previously discovered that pathogenic aPL recognize the cell surface protein β2-glycoprotein I (β2GPI) on endothelium, and that through intracellular signaling initiated by resulting β2GPI interaction with apolipoprotein E receptor 2 (apoER2), aPL antagonize endothelial NO synthase (eNOS) and thereby promote thrombosis. Seeking to develop a mechanism-based therapy, we determined if a blocking anti-β2GPI monoclonal antibody (mAb) can be identified that provides protection from aPL-induced thrombosis. Using bovine aortic endothelial cells, a series of anti-β2GPI mAbs was screened for their impact on VEGF-induced eNOS activity and their ability to prevent aPL antagonism of eNOS. aPL (polyclonal IgG) was isolated from APS patients and control normal human IgG (NHIgG) was obtained from healthy subjects. Certain anti-β2GPI mAb mimicked aPL and antagonized VEGF-induced eNOS activity, and others did not prevent aPL antagonism eNOS. However, a mAb to domain I of β2GPI designated 1N11 did not inhibit VEGF activation of eNOS and it fully prevented aPL antagonism of the enzyme. We then tested the ability of 1N11 to prevent thrombus formation induced by aPL using a mouse model of APS. C57BL/6 male mice received intraperitoneal injection of 1N11 or subtype-matched control IgG (C44) followed by injection of aPL or NHIgG twice, 24h apart. Thrombus formation in mesenteric arterioles was then quantified by intravital microscopy. In mice treated with the control mAb C44, aPL caused thrombi with a target size of 2 mm2 42% faster than NHIgG than NHIgG. The largest thrombus formed in 6 min was also 231% greater with aPL versus NHIgG. In contrast, in mice treated with the blocking mAb 1N11, aPL did not enhance the rapidity of thrombus formation or thrombus size. Thus, the mAb 1N11 directed against domain I of β2GPI ameliorates the adverse effects of aPL on endothelial cells in culture, and in mice it fully prevents aPL-induced thrombosis. As such, mechanism-based therapies targeting aPL recognition of β2GPI can be developed to combat APS.
- © 2013 by American Heart Association, Inc.