Role of beta 2-glycoprotein I and anti-phospholipid antibodies in activation of protein C in vitro.
OBJECTIVE
To investigate the effect of beta 2-glycoprotein I (beta 2 GPI) on the thrombin/thrombomodulin dependent activation of protein C; and to determine whether beta 2 GPI dependent anticardiolipin antibodies have any effect.


METHODS
Protein C was activated by thrombin in the presence of thrombomodulin and phospholipid vesicles in an in vitro system. The effect of adding purified beta 2 GPI to this system was observed. Affinity purified anticardiolipin antibodies and total IgG from patients with anticardiolipin antibodies and the lupus anticoagulant were studied for their effects on protein C activation in the presence and absence of beta 2 GPI.


RESULTS
beta 2-Glycoprotein I had no effect on the activity of preformed activated protein C. When the phospholipid vesicles were incubated with beta 2 GPI before the addition of protein C, the activation of protein C was inhibited in a dose dependent manner. With phosphatidylserine:phosphatidylcholine vesicles at a concentration of 1 microM:2 microM, beta 2 GPI began to inhibit the reaction at a concentration of 15 nM, and at 4 microM (the normal plasma concentration) the activation of protein C was reduced to 40%. Anticardiolipin antibodies had no demonstrable effect.


CONCLUSIONS
beta 2-Glycoprotein I inhibits protein C activation in an in vitro system. Its physiological role is unknown but it has potential procoagulant as well as anticoagulant properties. An effect of antiphospholipid antibodies on protein C activation, which might explain their association with thrombosis, could not be shown.
Keeling
D M
DM
Department of Haematology, University College and Middlesex School of Medicine, London.
Wilson
A J
AJ
Mackie
I J
IJ
Isenberg
D A
DA
Machin
S J
SJ
D017152:Antibodies, Antiphospholipid / Q000494:pharmacology*; D001053:Apolipoproteins / Q000494:pharmacology*; D001777:Blood Coagulation; D004305:Dose-Response Relationship, Drug; D005260:Female; D006023:Glycoproteins / Q000494:pharmacology*; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D066298:In Vitro Techniques; D008297:Male; D011485:Protein Binding; D011486:Protein C / Q000037:antagonists & inhibitors* / Q000378:metabolism; D053482:beta 2-Glycoprotein I
D017152:Antibodies, Antiphospholipid; D001053:Apolipoproteins; D006023:Glycoproteins; D007074:Immunoglobulin G; D011486:Protein C; D053482:beta 2-Glycoprotein I