Pathogenesis Of Enteric Viral Hepatitis

我们研究了病毒性肝炎的发病机制，以及这些重要病原体毒力和减毒的分子基础。我们已经证明甲型肝炎病毒(HAV)的毒力和减毒主要由两个基因控制：VP1/2A和2C。然而，衰减性突变在体内被强烈选择，导致出现毒力变异。这对甲型肝炎减毒活疫苗的研制具有重要意义。甲型肝炎的发病机制也正在通过基因芯片分析在黑猩猩模型中进行研究。先天反应和后天反应都已被记录下来。有趣的是，甲型肝炎病毒不会像丙型肝炎病毒和HDV感染那样强烈地触发某些干扰素刺激基因的上调。这是令人惊讶的，因为甲型肝炎病毒和丙型肝炎病毒都是单链RNA病毒，具有双链复制形式，而HDV是具有广泛碱基配对的单链病毒，被认为是双链RNA。具体地说，在2009财年，我们比较了几只实验感染甲型肝炎的黑猩猩的先天和获得性免疫反应，包括接受强毒疫苗接种的动物和感染甲型肝炎减毒株的动物。感染强毒株的动物有强大的先天免疫反应(尽管不如感染丙型肝炎病毒的黑猩猩那样强烈)，而在弱化感染中，这种反应不那么明显。有趣的是，在后一组黑猩猩中，先天免疫反应被缩短，但先天免疫反应的检测几乎与检测甲型肝炎病毒感染的特定血清学或分子探针一样敏感。也存在获得性免疫反应，但不如感染丙型肝炎病毒的黑猩猩的获得性免疫反应强。重要的是寻找病毒的控制机制，可能会阻止其中的一些系统。 尽管戊型肝炎在美国很少见，但它是亚洲、中东和北非成年人急性肝炎的最重要原因。像大多数肝炎病毒一样，它在细胞培养中复制很差，甚至根本不复制，并且不能传播给小型实验室动物。我们已经开发了用于在体外研究HEV的复制体；这些工具允许对病毒复制进行详细的分子分析，这可以通过分子工程病毒的感染性克隆在体内得到证实。此外，我们与同事们正在开发小型动物模型(猪的猪HEV，鸡的禽HEV)，利用HEV的非人类灵长类动物模型，为研究戊型肝炎病毒的相对发病机制提供了前所未有的机会。最后，还利用基因芯片对戊型肝炎进行了研究，发现了一种活跃的先天免疫反应，但获得性免疫反应较弱。具体地说，在2009财年，我们比较了几只黑猩猩对实验性HEV感染的先天和获得性免疫反应，以及在实验感染丙型肝炎病毒或甲型肝炎病毒的黑猩猩身上观察到的反应。与这些感染相比，HEV感染的特征是适应性免疫反应缩短和略有缩短。鉴于其他观察结果，HEV感染的抗体滴度往往比其他肝炎病毒感染的抗体滴度下降得更快，这一点特别有趣。

We have studied the pathogenesis of viral hepatitis and the molecular basis for virulence and attenuation of these important pathogens. We have shown previously that virulence and attenuation of hepatitis A virus (HAV) are controlled principally by two genes: VP1/2A and 2C. However, attenuating mutations are strongly selected against in vivo, resulting in the emergence of virulent variants. This has important implications for the development of live attenuated hepatitis A vaccines. The pathogenesis of hepatitis A is also being studied in the chimpanzee model by microarray analysis. Both innate and adaptive responses have been recorded. Interestingly, HAV does not trigger as robust an up-regulation of certain interferon stimulated genes as HCV and HDV infections. This is surprising because HAV and HCV are both single-stranded RNA viruses with a double-stranded replicative form and HDV is a single-stranded virus with extensive base pairing that is perceived as double-stranded RNA. Specifically, in FY 2009, we compared the innate and adaptive immune responses to HAV infection in several experimentally infected chimpanzees, including animals that received virulent inocula and those that were infected with attenuated strains of HAV. Animals infected with virulent strains had a robust innate immune response (although not as robust as that seen in HCV-infected chimpanzees), whereas the response was less marked in the attenuated infections. Interestingly, innate immune responses were abbreviated in the latter chimpanzees, but detection of the innate immune response was almost as sensitive a diagnostic test of infection as was detection of specific serologic or molecular probes of HAV infection. The adaptive immune responses were also present, but not as robust as the adaptive immune responses in HCV infections of chimpanzees. It will be important to search for viral mechanisms of control that may block some of these systems. Although rare in the United States, hepatitis E is the single most important cause of acute hepatitis among adults throughout Asia, the Middle East and North Africa. Like most of the hepatitis viruses, it replicates poorly or not at all in cell culture and cannot be transmitted to small laboratory animals. We have developed replicons for the study of HEV in vitro; these tools are permitting a detailed molecular analysis of viral replication that can be confirmed in vivo with molecularly engineered infectious cDNA clones of the virus. In addition, with colleagues, we are developing small animal models (swine HEV in swine, avian HEV in chickens) that, with nonhuman primate models of HEV, provide an unprecedented opportunity for studying the comparative pathogenesis of hepatitis E viruses. Finally, hepatitis E has also been studied by microarray and a brisk innate but weak adaptive immune response has been seen. Specifically, in FY 2009, we compared the innate and adaptive immune responses of several chimpanzees to experimental HEV infections with those observed in chimpanzees that had been experimentally infected with HCV or HAV. In comparison with those infections, HEV infections were characterized by an abbreviated and somewhat shortened adaptive immune response. This is particularly interesting in light of other observations that antibody titers tend to diminish more rapidly in HEV infections than in infections with the other hepatitis viruses.