de Laat Bas, van Berkel Miranda, Urbanus Rolf T, Siregar Berdien, de Groot Philip G, Gebbink Martijn F, Maas Coen
Department of Clinical Chemistry and Hematology, University Medical Center Utrecht, Utrecht, The Netherlands.
Arthritis Rheum. 2011 Dec;63(12):3960-8. doi: 10.1002/art.30633.
The presence of autoantibodies against a cryptic epitope in domain I of β(2)-glycoprotein I (β(2)GPI) is strongly associated with thrombotic events in patients with the antiphospholipid syndrome. We hypothesized that a conformational change could be a trigger for the formation of antibodies against domain I of β(2)GPI. Therefore, we investigated whether immune responses against β(2)GPI are related to its conformation.
Conformational changes in β(2)GPI were studied using various techniques, either upon binding to cardiolipin or after disruption of the internal disulfide bonds. The immunogenicity of β(2)GPI in different conformations as well as the individual domains of β(2)GPI were studied in vivo by monitoring the generation of antibodies after intravenous administration of β(2)GPI to mice. Furthermore, plasma samples from these mice were assessed for lupus anticoagulant activity and thrombin-antithrombin complex levels.
We observed that the interaction of β(2)GPI with cardiolipin induced a conformational change in β(2)GPI: electron microscopy revealed that β(2)GPI assembled into polymeric meshworks. We next investigated the immunogenicity of both human and murine β(2)GPI in mice. Both human and murine β(2)GPI combined with cardiolipin and misfolded β(2)GPI triggered antibody formation against the native protein as well as against domain I of β(2)GPI, while native β(2)GPI was not immunogenic. In addition, we observed that anti-domain I antibodies developed in mice injected with domain I of β(2)GPI, and that antibodies did not develop in mice injected with domains II-V. The induced anti-domain I antibodies prolonged the dilute Russell's viper venom plasma clotting time. The plasma of mice with anti-domain I antibodies had increased levels of circulating thrombin-antithrombin complexes.
The results of our studies indicate that the exposure of cryptic epitopes due to conformational changes in β(2)GPI can induce autoantibody formation.
抗β2糖蛋白I（β2GPI）结构域I中隐蔽表位的自身抗体的存在与抗磷脂综合征患者的血栓形成事件密切相关。我们推测构象变化可能是抗β2GPI结构域I抗体形成的触发因素。因此，我们研究了针对β2GPI的免疫反应是否与其构象有关。
使用各种技术研究β2GPI与心磷脂结合后或内部二硫键断裂后的构象变化。通过监测向小鼠静脉注射β2GPI后抗体的产生，在体内研究不同构象的β2GPI以及β2GPI各个结构域的免疫原性。此外，评估这些小鼠血浆样本的狼疮抗凝活性和凝血酶-抗凝血酶复合物水平。
我们观察到β2GPI与心磷脂的相互作用诱导了β2GPI的构象变化：电子显微镜显示β2GPI组装成聚合物网络。接下来，我们研究了人和鼠β2GPI在小鼠体内的免疫原性。人和鼠β2GPI与心磷脂结合以及错误折叠的β2GPI均引发了针对天然蛋白以及β2GPI结构域I的抗体形成，而天然β2GPI没有免疫原性。此外，我们观察到在注射β2GPI结构域I的小鼠中产生了抗结构域I抗体，而在注射结构域II-V的小鼠中未产生抗体。诱导产生的抗结构域I抗体延长了稀释的罗素蝰蛇毒血浆凝血时间。具有抗结构域I抗体的小鼠血浆中循环凝血酶-抗凝血酶复合物水平升高。
我们的研究结果表明，β2GPI构象变化导致隐蔽表位暴露可诱导自身抗体形成。
