Haemostasis Research Unit, University College London, 51 Chenies Mews, London WC1E 6HX, United Kingdom ; Centre for Haematology, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, United Kingdom.
Centre for Haematology, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, United Kingdom.
EBioMedicine. 2015 Jun 11;2(8):942-52. doi: 10.1016/j.ebiom.2015.06.007. eCollection 2015 Aug.
Acquired thrombotic thrombocytopenic purpura (TTP) is an autoimmune disease in which anti-ADAMTS13 autoantibodies cause severe enzyme deficiency. ADAMTS13 deficiency causes the loss of regulation of von Willebrand factor multimeric size and platelet-tethering function, which results in the formation of disseminated microvascular platelet microthrombi. Precisely how anti-ADAMTS13 autoantibodies, or antibody subsets, cause ADAMTS13 deficiency (ADAMTS13 activity generally < 10%) has not been formally investigated.
We analysed 92 acquired TTP episodes at presentation, through treatment and remission/relapse using epitope mapping and functional analyses to understand the pathogenic mechanisms of anti-ADAMTS13 IgG.
89/92 of TTP episodes had IgG recognising the ADAMTS13 N-terminal domains. The central spacer domain was the only N-terminal antigenic target detected. 38/92 TTP episodes had autoantibodies recognising the N-terminal domains alone; 54/92 TTP episodes also had antibodies against the ADAMTS13 C-terminal domains (TSP2-8 and/or CUB domains). Changes in autoantibody specificity were detected in 9/16 patients at relapse, suggesting a continued development of the disease. Functional analyses on IgG from 43 patients revealed inhibitory IgG were limited to anti-spacer domain antibodies. However, 15/43 patients had autoantibodies with no detectable inhibitory action and as many as 32/43 patients had autoantibodies with inhibitory function that was insufficient to account for the severe deficiency state, suggesting that in many patients there is an alternative pathogenic mechanism. We therefore analysed plasma ADAMTS13 antigen levels in 91 acquired TTP presentation samples. We demonstrated markedly reduced ADAMTS13 antigen levels in all presentation samples, median 6% normal (range 0-47%), with 84/91 patients having < 25% ADAMTS13 antigen. ADAMTS13 antigen in the lowest quartile at first presentation was associated with increased mortality (odds ratio 5.7).
Anti-spacer domain autoantibodies are the major inhibitory antibodies in acquired TTP. However, depletion of ADAMTS13 antigen (rather than enzyme inhibition) is a dominant pathogenic mechanism. ADAMTS13 antigen levels at presentation have prognostic significance. Taken together, our results provide new insights into the pathophysiology of acquired TTP.
获得性血栓性血小板减少性紫癜（TTP）是一种自身免疫性疾病，其中抗 ADAMTS13 自身抗体导致严重的酶缺乏。ADAMTS13 缺乏导致 von Willebrand 因子多聚体大小和血小板结合功能失去调节，从而导致弥散性微血管血小板微血栓形成。抗 ADAMTS13 自身抗体或抗体亚群如何导致 ADAMTS13 缺乏（ADAMTS13 活性通常 <10%）尚未得到正式研究。
我们通过表位作图和功能分析，分析了 92 例获得性 TTP 发作时、治疗中和缓解/复发时的情况，以了解抗 ADAMTS13 IgG 的致病机制。
89/92 例 TTP 发作的 IgG 识别 ADAMTS13 N 端结构域。中央间隔区是唯一检测到的 N 端抗原靶标。38/92 例 TTP 发作的 IgG 仅识别 N 端结构域；54/92 例 TTP 发作的 IgG 也识别 ADAMTS13 C 端结构域（TSP2-8 和/或 CUB 结构域）。9/16 例患者在复发时检测到自身抗体特异性的变化，提示疾病的持续发展。对 43 例患者 IgG 的功能分析表明，抑制性 IgG 仅限于抗间隔区抗体。然而，15/43 例患者的自身抗体没有检测到抑制作用，多达 32/43 例患者的自身抗体具有抑制作用，但不足以解释严重缺乏状态，这表明在许多患者中存在替代的致病机制。因此，我们分析了 91 例获得性 TTP 发作时样本的血浆 ADAMTS13 抗原水平。我们证明，所有发作样本的 ADAMTS13 抗原水平均显著降低，中位数为正常的 6%（范围 0-47%），84/91 例患者的 ADAMTS13 抗原 <25%。初次就诊时 ADAMTS13 抗原处于最低四分位数与死亡率增加相关（优势比 5.7）。
抗间隔区自身抗体是获得性 TTP 的主要抑制性抗体。然而，ADAMTS13 抗原的耗竭（而非酶抑制）是一种主要的致病机制。初次就诊时的 ADAMTS13 抗原水平具有预后意义。总之，我们的研究结果为获得性 TTP 的病理生理学提供了新的见解。
