Pathogenesis Of Enteric Viral Hepatitis

我们已经研究了病毒性肝炎的发病机制和这些重要病原体的毒力和减毒的分子基础。我们以前已经表明，甲型肝炎病毒（HAV）的毒力和减毒主要由两个基因控制：VP 1/2A和2C。然而，减毒突变在体内被强烈选择，导致毒性变体的出现。这对甲型肝炎减毒活疫苗的开发具有重要意义。甲型肝炎的发病机制也正在通过微阵列分析在黑猩猩模型中研究。先天反应和适应性反应都有记录。有趣的是，HAV不会像HCV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HAV和HCV都是具有双链复制形式的单链RNA病毒，而HDV是具有广泛碱基配对的单链病毒，其被认为是双链RNA。 具体来说，在2009财年，我们比较了先天性和适应性免疫反应，甲型肝炎病毒感染的几个实验感染的黑猩猩，包括动物接受强毒接种和那些被感染的甲型肝炎病毒减毒株。 感染了强毒株的动物有一个强大的先天免疫反应（虽然不像HCV感染的黑猩猩那样强大），而这种反应在减毒感染中不那么明显。 有趣的是，先天免疫反应在后者的黑猩猩中被缩短，但先天免疫反应的检测几乎是敏感的感染诊断试验，因为是检测HAV感染的特异性血清学或分子探针。 也存在适应性免疫应答，但不如黑猩猩HCV感染中的适应性免疫应答那么强。重要的是要寻找病毒的控制机制，可能会阻止这些系统中的一些。 虽然在美国很少见，但戊型肝炎是整个亚洲，中东和北非成人急性肝炎的唯一最重要原因。 像大多数肝炎病毒一样，它在细胞培养中复制很差或根本不复制，并且不能传播给小型实验室动物。我们已经开发了复制子的研究戊型肝炎病毒在体外，这些工具是允许一个详细的病毒复制的分子分析，可以在体内证实与分子工程感染性的cDNA克隆的病毒。 此外，我们正在与同事一起开发小动物模型（猪中的猪HEV，鸡中的禽HEV），这些模型与HEV的非人灵长类动物模型一起，为研究戊型肝炎病毒的比较发病机制提供了前所未有的机会。 最后，戊型肝炎也通过微阵列进行了研究，并且已经看到了活跃的先天性但弱的适应性免疫应答。 具体来说，在2009财年，我们将几只黑猩猩对实验性戊型肝炎病毒感染的先天性和适应性免疫反应与在实验性感染丙型肝炎病毒或甲型肝炎病毒的黑猩猩中观察到的免疫反应进行了比较。 与这些感染相比，戊型肝炎病毒感染的特点是缩短和稍微缩短适应性免疫反应。 这是特别有趣的，鉴于其他观察结果，抗体滴度往往减少更迅速地在HEV感染比感染其他肝炎病毒。

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.