Anti-endothelial cell antibody binding makes negatively charged phospholipids accessible to antiphospholipid antibodies

Abstract

Objective: Anti-endothelial cell autoantibodies (AECA) are often associated with antibodies to anionic phospholipids (PL), such as phosphatidylserine (PS). Yet, beta2-glycoprotein I (beta2GPI)-dependent anti-PL antibodies (aPL) do not have access to their target antigens on the membrane of endothelial cells (EC). Given that AECA are capable of exposing PS and, thereby, initiating apoptosis, we explored the relationships between AECA, beta2GPI, and aPL on the surface of EC.

Methods: Human EC were incubated with mouse AECA monoclonal antibodies, and the translocation of PS was established through the binding of annexin V, which binds specifically to PS. A rabbit anti-beta2GPI antibody and biotin-conjugated F(ab')2 aPL derived from 3 patients were also used to detect beta2GPI on the cells.

Results: Twenty percent to 36% of the cells expressed anionic PL following incubation with AECA, as revealed by the binding of annexin V and beta2GPI. The proportion of anionic PL-expressing EC (up to 90%) correlated with the period of incubation of EC with AECA and depended on the dose of AECA. Bound aPL resided exclusively within the AECA-positive EC population.

Conclusion: Based on our findings, AECA may be pathogenic. Some of them may even have the potential to induce production of aPL.