Department of Haematology, Addenbrooke's Hospital, Cambridge University Hospitals NHS Trust, Cambridge, UK.
Department of Haematology, Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK.
J Thromb Haemost. 2016 Jan;14(1):137-42. doi: 10.1111/jth.13171. Epub 2015 Dec 29.
ESSENTIALS: An IgA paraprotein with anti-thrombin activity was not associated with a severe bleeding phenotype. This observation challenges the paradigm that anticoagulant therapy necessarily increases bleeding risk. Characterization of the antibody showed that it specifically binds to thrombin exosite I. A therapeutic drug with the properties of this antibody might be an antithrombotic that doesn't cause bleeding.
We report the case of a 54-year-old female who presented with a traumatic subdural hemorrhage. Coagulation tests were markedly prolonged due to the presence of an anti-thrombin IgA paraprotein at 3 g L(-1) . The patient made a complete recovery and has had no abnormal bleeding during a 7-year follow-up, despite the persistence of the paraprotein.
To determine how the paraprotein prolonged clotting tests by defining its target and its epitope.
The paraprotein was purified and added to normal pooled plasma for in vitro clotting assays. Binding studies were conducted to determine the affinity of the IgA for thrombin. The Fab was isolated and crystallized with thrombin.
The purified IgA was sufficient to confer the patient's in vitro coagulation profile in normal pooled plasma, and was found to bind specifically and with high affinity to thrombin. A crystal structure of the Fab fragment in complex with thrombin revealed an exosite I interaction involving CDRH3 of the antibody.
Although the patient originally presented with a subdural bleed, the hematoma resolved without intervention, and no other bleeding event occurred during the subsequent 7 years. During this period, the patient's IgA paraprotein levels have remained constant at 3 g L(-1) , suggesting that the presence of a high-affinity, exosite I-directed antibody is consistent with normal hemostasis. A therapeutic derivative of this antibody might therefore permit antithrombotic dose escalation without an associated increase in the risk of bleeding.
我们报告了一例 54 岁女性因创伤性硬脑膜下血肿就诊的病例。由于存在 3 g/L 的抗凝血酶 IgA 副蛋白，凝血测试明显延长。尽管存在副蛋白，但患者完全康复，并且在 7 年的随访期间没有异常出血。
通过确定副蛋白的靶标和表位，确定其如何延长凝血测试。
将副蛋白纯化并添加到正常混合血浆中进行体外凝血测定。进行结合研究以确定 IgA 与凝血酶的亲和力。分离 Fab 并与凝血酶结晶。
纯化的 IgA 足以赋予正常混合血浆中的患者体外凝血谱，并且发现其特异性结合并具有高亲和力与凝血酶结合。与凝血酶的 Fab 片段晶体结构揭示了涉及抗体 CDRH3 的外位 I 相互作用。
尽管患者最初表现为硬脑膜下出血，但血肿未经干预自行消退，并且在随后的 7 年内没有发生其他出血事件。在此期间，患者的 IgA 副蛋白水平一直保持在 3 g/L，这表明存在高亲和力、外位 I 定向抗体与正常止血一致。因此，这种抗体的治疗衍生物可能允许在不增加出血风险的情况下增加抗血栓形成剂量。
