戊型肝炎病毒分泌型衣壳蛋白的结构与功能探究

Hepatitis E virus (HEV) is one of the leading causes of acute viral hepatitis in the worldwide. The mortality rate can reach as high as 20-30% in high-risk population, such as pregnant women, the elderly and patients with chronic liver disease. The epidemiological studies showed that, although the positive rate of HEV seroprevalence was higher in the elderly, the elderly were still susceptible to hepatitis E. It indicated an immune escape mechanism presented in HEV infection. We found that HEV produced a secreted protein pORF2S during replication, which is homologous to the HEV capsid protein pORF2C. The pORF2S but has an individual expression pathway and does not participate in construction of virions. Based on previous research results and clinical reports, we found that pORF2S may play an important role in the HEV immune escape, reinfection and chronicity. Therefore, this project intends to elucidate the role of pORF2S in viral infection and host antibody responses by analyzing the structure of pORF2S, identifying its key epitopes and comparing it with capsid protein pORF2C, and studying the function of pORF2S in vitro and vivo models. By trying to reveal the relationship between the pORF2S and HEV immune escape, we attempt to provide a theoretical basis for the prevention and treatment of HEV in immunocompromised populations.

戊型肝炎病毒(HEV)是全球范围内急性病毒性肝炎的最主要诱因之一，在高危人群中（孕妇、老年人和慢性肝病患者）死亡率可高达20~30﹪。流行病毒学研究结果显示虽然高龄人群中HEV血清阳性率较高，但老年人依然为戊肝的易感人群，表明HEV存在免疫逃逸机制。本课题组发现HEV在复制过程中会产生一种分泌型蛋白pORF2S，该蛋白与HEV衣壳蛋白pORF2C同源，但存在完全不同的表达途径且不参与病毒组装。本课题组结合前期研究结果及部分临床报道，发现pORF2S可能在HEV免疫逃逸、重复感染及慢性化过程中起重要作用。因此本课题拟通过对pORF2S进行结构解析，鉴定其关键性表位，并对比与衣壳蛋白pORF2C的异同，通过体内外模型深入研究pORF2S的潜在功能，阐明pORF2S在病毒感染及机体抗体应答过程中的作用，揭示pORF2S与HEV免疫逃逸的相关性，为HEV在免疫力低下人群中的预防与治疗提供理论依据。

HEV是全球范围内急性病毒性肝炎最主要的病原体之一，在一些发展中国家是50%的急性病毒性肝炎病例的诱发病原。在老年人等免疫系统下调或受抑制的人群中，血清IgG阳性不能完全抑制HEV的感染，并且该人群感染HEV往往容易导致更为严重的症状，提示HEV可能存在潜在的抗体应答逃逸机制。HEV患者血清中的病毒颗粒以含包膜的形式存在，但血清中的pORF2抗原能被抗体检测到，并且与RNA之间无明显的相关性，提示血清中可能存在其他未被鉴定的pORF2蛋白。本研究通过分离纯化pORF2S蛋白，鉴定其表位，比较与pORF2C的表位异同并进行了pORF2S的结构解析，探究了差异表位产生的分子机制； 基于HEV细胞模型，探究了pORF2S在病毒感染吸附、蛋白质翻译阶段的影响，探究了pORF2s对于中和抗体及血清中和的影响，阐明了pORF2S对于病毒在血清中和抗体逃逸中的潜在功能；基于动物免疫，探究了机体对大量存在的pORF2S蛋白产生的抗体免疫应答，与感染性病毒颗粒上的衣壳蛋白pORF2C的抗体应答差异，阐明pORF2S与HEV免疫逃逸的相关性。