β ₂-Glycoprotein I and anticardiolipin antibody binding to resting and activated cultured human endothelial cells

Objective. To examine β ₂-glycoprotein I (β ₂-GPI) binding and its ability to augment IgG anticardiolipin (aCL) antibody binding to resting and cytokine activated endothelial cells in vitro. To evaluate the ability of IgG aCL antibody positive sera to induce endothelial cell activation in vitro. Methods. IgG with aCL activity was isolated by affinity purification from 6 patients with systemic lupus erythematosus (SLE) and 3 patients with primary antiphospholipid antibody syndrome (APS). Human umbilical vein endothelial cells (HUVEC) were cultured in serum-free conditions and examined in a resting state or after activation with tumor necrosis factor alpha (TNF-α). HUVEC were exposed to β ₂-GPI alone, IgG alone or IgG plus β ₂-GPI. Finally, we examined the ability of sera from the same patients with SLE and primary APS to activate HUVEC in culture. Results. Neither β ₂-GPI, IgG aCL, nor IgG aCL plus β ₂-GPI bound to resting or cytokine activated endothelial cells. In addition, sera from the same patients did not induce in vitro activation of endothelial cells as assessed by enhanced surface expression of intercellular adhesion molecule, vascular cell adhesion molecule, and E-selectin. Conclusion. Results suggest that β ₂-GPI deposition on either resting or activated endothelial cells and modulation of its proposed in vivo anticoagulant activity through subsequent aCL antibody binding does not account for the thrombotic manifestations of APS.