Effects of β₂‐glycoprotein I and monoclonal anticardiolipin antibodies in platelet interaction with subendothelium under flow conditions

Abstract

Objective. To evaluate whether the effect of human monoclonal anticardiolipin antibodies (aCL) on platelet interaction with the subendothelium under flow conditions is dependent on ␤ 2 -glycoprotein I (␤ 2 GPI).Methods. Three monoclonal IgM aCL with anti-␤ 2 GPI activity (TM1B3, GR1D5, and EY2C9) obtained from patients with antiphospholipid syndrome, a monoclonal aCL with lupus anticoagulant activity but without anti-␤ 2 GPI activity (FRO) obtained from a patient with a splenic lymphoma, and a control monoclonal IgM without aCL activity were used. TM1B3, GR1D5, EY2C9, FRO, and control IgM (30 g/ml) were added to reconstituted blood containing gel-filtered platelets (200 ؋ 10 9 /liter), factor VIII (100 units/dl), and fibrinogen (1.5 gm/liter). Samples were perfused (wall-shear rate 800 seconds ؊1 ), with and without the addition of purified ␤ 2 GPI (20 g/ml), through annular chambers containing collagen-rich denuded vascular segments, and the percentages of surface covered by platelets and by thrombi were evaluated.Results. No differences in the percentages of surface covered by platelets and by thrombi were observed among samples with TM1B3, GR1D5, EY2C9, FRO, and control IgM added when reconstituted blood samples without ␤ 2 GPI were used. However, a significant increase in the percentage of surface covered by platelets was observed in the presence of TM1B3, GR1D5, and EY2C9 but not in the presence of FRO when samples containing ␤ 2 GPI were used. Increased thrombi formation was induced by TM1B3 and GR1D5 but not by EY2C9 or FRO in samples with added ␤ 2 GPI.Conclusion. Monoclonal aCL require anti-␤ 2 GPI activity to promote platelet interaction with the subendothelium under flow conditions.

Mechanism of Thrombosis in Antiphospholipid Syndrome: Binding to Platelets

“…Similar results were obtained in the same system when the experiments were performed using human monoclonal anticardiolipin (anti-β 2 -glycoprotein I) antibodies [17], and the β 2 -glycoprotein-dependence of this phenomenon has been evidenced [18]. Additionally, dimers of β 2 -glycoprotein I, that mimic effects of β 2 -glycoprotein I-anti-β 2 -glycoprotein I antibody complexes, have been found to increase platelet adhesion and thrombus formation in a flow system but not increased aggregation in an aggregometer [19].…”

“…Moreover, it has been demonstrated [18], using reconstituted blood in flowing systems that simulate physiological conditions β 2 -glycoprotein, that the β 2 -glycoprotein dependence of the increased platelet-vessel wall interaction induced by human monoclonal anti-β 2 -glycoprotein I antibodies obtained from patients with APS. In addition, it has been reported [8] that murine monoclonal antibodies against β 2 -glycoprotein I with LA activity potentiate the effect of sub-threshold concentrations of aggregation agonists (ADP or adrenaline) but requiring the presence of β 2 -glycoprotein I.…”

Further Investigations of the Effects of Anti-β2GP1 Antibodies on Collagen-Induced Platelet Aggregation

“…It may be that anti-β 2 GP1–β 2 GP1 complexes only promote platelet interaction with collagen under more physiological flow conditions. 25 Moreover, anti-β 2 GP1 antibodies may require additional exogenous β 2 GP1 to activate platelets. 26…”

Antiphospholipid syndrome: multiple mechanisms

“…Activation of platelets has been shown in an in vitro model, using polyclonal and monoclonal aPL from patients with APS [77]. It has also been shown in a different model that anti β 2 GPI antibodies can promote platelet binding to vascular subendothelium [78]. Another group has found that complexes of aPL and β 2 GPI can increase the production from platelets of thromboxane A2, an eicosanoid that promotes vasoconstriction and clotting [79].…”