补体H因子在抗中性粒细胞胞浆抗体相关小血管炎发病机制中的研究

The pathogenesis of antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) has not been fully understood. ANCA and neutrophils had been demonstrated to play an important role in the process of AAV. Our previous studies found that alternative complement pathway activation played an important role in the pathogenesis of human ANCA-associated vasculitis. Since complement factor H is one of the key regulator in alternative pathway, we were interested in its role in the pathogenesis of ANCA-associated vasculitis and conducted a series of experiments. It revealed that the binding between mCRP and complement factor H, which can inhibit the alternative complement pathway activation, could be blocked by MPO, which was released from ANCA activated neutrophils. It reminded us that complement factor H might take part in the pathogenesis of ANCA-associated vasculitis. According to the previous results, we propose this scientific hypothesis: complement factor H might play an important role in the pathogenesis of ANCA associated vasculitis. The role may be through over activation of alternative complement pathway caused by low levels or deficiency in bio-function of plasma complement factor H, which might be caused by plasma anti-factor H antibodies or complement factor H mutation. The research will be completed by detecting plasma levels of complement factor H, plasma levels of circulating autoantibodies against complement factor H and bio-function and genes of complement factor H in patients with ANCA-associated vasculitis.

抗中性粒细胞胞浆抗体（ANCA）相关小血管炎发病机制目前未明，ANCA和中性粒细胞在其中起重要作用。申请者前期研究发现补体旁路活化是本病发病机制中的重要环节。鉴于H因子是补体旁路途经中重要的负向调节因子，我们推测H因子的异常可能参与了本病的发病机制。我们的前期研究发现在ANCA相关小血管炎患者中， ANCA活化的中性粒细胞释放的髓过氧化物酶可阻断C反应蛋白和H因子的结合，可能干扰H因子在补体旁路途径中的负调节作用，提示H因子可能参与了本病发病。因此我们提出如下假设：在ANCA相关小血管炎中可能存在H因子的异常，导致补体旁路途径过度活化，参与本病的发病。本研究拟进行ANCA相关小血管炎患者外周血中H因子水平及功能、抗H因子抗体水平检测，以及ANCA相关小血管炎患者H因子遗传背景检测。明确是否存在H因子水平异常或功能缺陷，并研究上述异常是否由于H因子遗传背景的突变或循环中出现抗H因子抗体造成。

补体旁路活化是抗中性粒细胞胞浆抗体（Anti-Neutrophil Cytoplasmic Antibody, ANCA）相关小血管炎发病机制中的重要环节，而H因子是补体旁路活化负向调节的关键蛋白，本课题组推测在ANCA相关小血管炎中可能存在补体H因子的异常。通过研究发现，活动期ANCA相关小血管炎患者存在血浆H因子水平的降低，血浆H因子水平与患者的疾病活动度存在相关性，并且在某种程度上对这部分患者的复合终点事件有预测意义。后续功能学实验发现ANCA阳性血管炎患者表现出H因子功能活性的缺陷，包括调节C3b 的功能、与mCRP 的结合功能、与内皮细胞的结合功能，及抑制绵羊红细胞溶血的功能。同时，我们发现H因子辅助I因子活性与ANCA相关小血管炎患者循环中Bb（补体旁路途径活化所特有的因子）以及可溶性C5b-9水平负相关, 与循环C5a的水平存在负相关趋势；H因子与mCRP的结合能力与伯明翰血管炎活动度评分（Birmingham vasculitis activity score, BVAS）负相关；H因子抑制补体介导的绵羊红细胞溶血的能力与血浆可溶性C5b-9的水平负相关。以上结果提示H因子的功能缺陷可导致补体旁路途径活化，可能参与ANCA相关小血管炎发病。本课题组对ANCA相关小血管炎患者H因子功能异常的原因进行了进一步研究。发现在ANCA相关小血管炎中，中性粒细胞被ANCA活化后释放的MPO能与H因子直接结合（结合的位点主要位于N端SCR1-4），并影响H因子的补体调节功能：MPO明显抑制H因子与C3b结合，并进一步抑制H因子降解旁路途径C3转化酶的能力。H因子在液相，肾小球内皮细胞表面，以及ECM表面辅助I因子裂解C3b的能力均明显被MPO抑制。虽然MPO不影响H因子保护绵羊红细胞溶血的功能，但是上清中的C3a和C5a均明显升高。MPO与H因子间的作用可以在一定程度上解释ANCA相关小血管炎患者H因子功能缺陷的原因。