Pathogenesis of Parenteral Viral Hepatitis

我们正在研究病毒性肝炎的发病机制以及这些重要病原体的毒力和减毒的分子基础。 在与Frank Chisari博士（Scripps研究所）的合作研究中，我们在黑猩猩中研究了宿主清除B型肝炎病毒感染的机制以及这些机制与临床疾病的关系。我们证明，清除HBV合成的模板，共价闭合的环状HBV DNA，从肝细胞中消除的非细胞溶解机制，主要由干扰素γ在肝脏中介导。含有HBV抗原的残留肝细胞的消除是由细胞溶解性CD 8阳性T细胞介导的后期事件，并且与感染的肝炎阶段时间相关。通过对黑猩猩感染B型肝炎过程中上调和下调的肝内信使RNA的微阵列分析，进一步研究了急性B型肝炎病毒诱导和免疫应答相关基因的谱。令人惊讶的是，我们无法检测到对感染的先天性免疫应答的证据，这表明HBV可以破坏宿主免疫应答，但我们确实在感染的清除阶段检测到强烈的适应性免疫应答;这与上述病毒复制的抑制和感染细胞的清除相关。有趣的是，在对黑猩猩慢性HBV感染的其他研究中，我们发现了一种先天免疫反应，这种反应在HBV的急性自限性感染中缺失。 这发生在肝损伤的时候，表明从死亡和垂死的肝细胞释放的病毒和细胞产物可以触发其他先天宿主防御，如TLR-3。然而，上调的先天免疫反应较弱，不足以影响病毒复制。 丙型肝炎病毒的遗传异质性被认为在其致病性中起重要作用。我们以前已经研究了这种关系，通过确定从输血后感染的患者中回收的HCV分离株的遗传异质性，以研究感染的早期阶段，以及从接受干扰素治疗的患者中回收的HCV分离株，以研究慢性感染后期的变化。在感染的最初几周内，观察到病毒克隆序列动态变化的独特模式，这些模式与感染的结果相关。同样，干扰素治疗期间序列的动态变化模式可预测结果。这些发现可能有助于在治疗过程中早期预测干扰素治疗的结果。 虽然已经从这些患者的纵向研究中获得了相当多的信息，但很难研究这些系统中的发病机制。黑猩猩是除人类以外唯一易感染HCV的动物，为研究宿主和病毒在丙型肝炎发病机制中的相互作用提供了实验模型。与Frank Chisari的合作研究表明，与B型肝炎病毒感染一样，在丙型肝炎病毒感染中，细胞免疫应答在病毒复制的非溶细胞下调和残留感染细胞的溶细胞清除中起重要作用。这两种机制是连续的和重叠的，前者似乎是由干扰素γ介导的，后者是由CD 8阳性细胞介导的，并且可能是由干扰素γ通过其促炎活性介导的。这些研究还揭示了1型干扰素（干扰素α/β）激活的抗病毒蛋白在应答病毒感染时表达，但HCV对这种先天免疫应答的抗病毒活性具有抗性。微阵列研究宿主对病毒性肝炎的免疫反应以及肝炎病毒如何试图规避反应，正在产生关于这些疾病发病机制的重要信息，并且该研究正在扩展到其他肝炎病毒，以描述这些试剂在单一宿主黑猩猩中的比较发病机制，黑猩猩是唯一对所有人类肝炎病毒敏感的非人类宿主。 目前，我们也正在研究HDV感染的发病机制，通过微阵列分析，并确定了先天性和适应性免疫反应，这样的感染。对HDV感染的免疫应答与我们在HCV感染期间观察到的免疫应答相似：既有强烈的先天性免疫应答，也有强烈的适应性免疫应答。 先天免疫反应足以下调HBV慢性感染的黑猩猩与HDV重叠感染的HBV复制。因此，HBV虽然不能触发先天性免疫应答，但当由另一种病毒提供时，对这种应答高度敏感。

We are studying the pathogenesis of viral hepatitis and the molecular basis for virulence and attenuation of these important pathogens. In collaborative studies with Dr. Frank Chisari (Scripps Institute) we have studied in chimpanzees the mechanism by which the host clears a hepatitis B virus infection and the relationship of these mechanisms to clinical disease. We demonstrated that the clearance of the template for HBV synthesis, covalently closed circular HBV DNA, is eliminated from hepatocytes by non-cytolytic mechanisms mediated principally by interferon gamma in the liver. Elimination of residual hepatocytes containing HBV antigens is a later event that is mediated by cytolytic CD8 positive T cells and is temporally related to the hepatitis phase of the infection. The spectrum of virus-induced and immune response-related genes involved in acute hepatitis B were further studied by microarray analysis of intrahepatic messenger RNAs up-regulated and down-regulated during the course of hepatitis B infections in chimpanzees. Surprisingly, we could not detect evidence of an innate immune response to infection, suggesting that HBV can subvert the host immune response, but we did detect a strong adaptive immune response during the clearance phase of infection; this correlated with the inhibition of viral replication and removal of infected cells described above. Interestingly, in additional studies of chronic HBV infection in chimpanzees, we found an innate immune response that was missing in acute, self-limiting infections of HBV. This occurred at a time of liver damage, suggesting that viral and cellular products released from dead and dying hepatocytes could trigger other innate host defenses, such as TLR-3. However, the up-regulated innate immune responses were weak and insufficient to affect virus replication. The genetic heterogeneity of hepatitis C virus is believed to play an important role in its pathogenicity. We have previously examined this relationship by determining the genetic heterogeneity of HCV isolates that were recovered from patients who were infected following transfusion in order to study the early phase of infection and from patients undergoing interferon therapy in order to study changes during the later phase of chronic infection. Distinctive patterns of dynamic change in the sequence of viral clones during the first several weeks of infection were observed and these correlated with the outcome of infection. Similarly, the pattern of dynamic changes in sequence during interferon therapy was predictive of the outcome. These findings may be useful in predicting the outcome of therapy with interferon early in the course of treatment. Although considerable information has been gained from these longitudinal studies of patients, it is difficult to study the mechanisms of pathogenesis in such systems. Chimpanzees, which are the only animals other than man that are susceptible to infection with HCV, provide an experimental model for studying the interactions of the host and the virus in the pathogenesis of hepatitis C. Collaborative studies with Frank Chisari have demonstrated that, as in hepatitis B virus infections, in hepatitis C virus infections the cellular immune response plays an important role in noncytolytic down-regulation of viral replication and cytolytic removal of residual infected cells. These two mechanisms are sequential and overlapping and the former appears to be mediated by interferon gamma and the latter by CD8 positive cells and, perhaps by interferon gamma through its proinflammatory activity. These studies have also revealed that type 1 interferon (interferon alpha/beta)-activated antiviral proteins are expressed in response to the viral infections, but that HCV is resistant to the antiviral activity of this innate immune response. Microarray studies of the host immune responses to viral hepatitis and how the hepatitis viruses attempt to circumvent the responses, are yielding important information on pathogenesis of these diseases, and the studies are being extended to the other hepatitis viruses in order to delineate the comparative pathogenesis of these agents in a single host, the chimpanzee, which is the only non-human host that is susceptible to all human hepatitis viruses. Currently, we are also studying the pathogenesis of HDV infections by microarray analysis and have identified both innate and adaptive immune responses to such infections. Immune responses to HDV infection were similar to those we observed during HCV infection: both a strong innate and a strong adaptive immune response. The innate immune response was sufficient to down-regulate HBV replication in HBV chronically infected chimpanzees that were superinfected with HDV. Thus, HBV, although unable to trigger an innate immune response, is highly sensitive to such a response when provided by another virus.