title: Inhibition of APC anticoagulant activity on oxidized phospholipid by anti-{beta}2-glycoprotein I monoclonal antibodies.
abstract: Activated protein C (APC) anticoagulant activity and the ability to be inhibited by auto-antibodies associated with thrombosis are strongly augmented by the presence of phosphatidylethanolamine (PE) and phospholipid oxidation. beta(2)-glycoprotein I (beta(2)-GPI) is a major antigen for antiphospholipid antibodies present in patients with the antiphospholipid syndrome. We therefore investigated whether anti-beta(2)-GPI monoclonal antibodies (mAbs) could inhibit APC with similar membrane specificity. Five mouse mAbs that reacted with different epitopes on beta(2)-GPI were examined. Each inhibited the PE-, phospholipid oxidation-dependent enhancement of APC anticoagulant activity and required antibody divalency. A chimeric APC that retains anticoagulant activity but is relatively unaffected by protein S, PE, or oxidation was not inhibited by the antibodies. In purified systems, anti-beta(2)-GPI mAb inhibition of factor Va inactivation was greater in the presence of protein S and required beta(2)-GPI. Surprisingly, although the mAbs did increase beta(2)-GPI affinity for membranes, PE and oxidation had little influence on the affinity of the beta(2)-GPI antibody complex for the membrane vesicles. We conclude that antibodies to beta(2)-GPI inhibit APC function specifically and contribute to a hypercoaguable state by disrupting specific protein-protein interactions induced by oxidation of PE-containing membranes.
authors.affiliation: Cardiovascular Biology Research Program, Oklahoma Medical Research Foundation, 825 NE 13th St, Oklahoma City, OK 73104, USA.
authors.forename: Omid
authors.initials: O
authors.lastname: Safa
authors.forename: Charles T
authors.initials: CT
authors.lastname: Esmon
authors.forename: Naomi L
authors.initials: NL
authors.lastname: Esmon
mesh_terms: D000818:Animals; D017152:Antibodies, Antiphospholipid / Q000494:pharmacology*; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D000925:Anticoagulants / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006023:Glycoproteins / Q000037:antagonists & inhibitors / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D010084:Oxidation-Reduction; D010743:Phospholipids / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011486:Protein C / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors; D053482:beta 2-Glycoprotein I
chemical_list: D017152:Antibodies, Antiphospholipid; D000911:Antibodies, Monoclonal; D000925:Anticoagulants; D006023:Glycoproteins; D010743:Phospholipids; D011486:Protein C; D053482:beta 2-Glycoprotein I