Immunobiology Of Scrapie Virus Infection

传染性海绵状脑病（TSE）疾病影响范围广泛的物种，包括羊，牛，水貂，人类，鹿，麋鹿等。一个特别重要的问题是确定哪些TSE疾病可以传播给其他物种，特别是人类或牲畜。为了研究跨物种传播的问题，我们使用了一种动物模型，该模型涉及仓鼠瘙痒症因子对小鼠的传播（在我们的研究之前，小鼠被认为对仓鼠瘙痒症具有抗性）。我们发现，在假定不相容的宿主之间可以发生跨物种传播，但涉及一个非常缓慢但无情的过程，需要在新宿主中进行几次传代，然后才最终成为一种可识别的疾病。这种持久性和最终的适应表明，类似的情况可能发生在其他物种的组合。 在美国，人们担心鹿和麋鹿的慢性消耗性疾病可能通过类似的机制传染给人类或其他物种。为了研究这种特殊的可能性，我们给非人灵长类动物接种了CWD感染的大脑。如果非人类的灵长类动物生病了，那么人类也可能易感。几只动物在大约26个月前接种，但没有显示出任何TSE样疾病的临床证据。动物通过脑内或经口途径接种。为了研究慢性消耗病的其他方面，我们已经开发了鹿朊蛋白转基因小鼠。已经衍生出几个系，使鹿PrPsen和接种后CWD脑匀浆来自CWD感染的鹿或麋鹿发展临床疾病和疾病相关的PrP-res。这些小鼠被用来研究CWD的几个方面，包括在感染动物的发病机制和持久性是否发生在看似未感染的动物。它们还被用于开发在自然感染动物或动物模型中发现的CWD感染性的测定。 在过去的几年里，其他几种转基因小鼠已被用于研究朊病毒蛋白对种间传播的影响，特定细胞类型对TSE发病机制和疾病发展动力学的作用等各种问题。已知种间传播可能涉及所涉及物种的朊病毒蛋白（PrP）之间的朊病毒蛋白相互作用。为了确定PrP如何影响物种间的传播，我们开发了仓鼠朊蛋白（HPrP）转基因小鼠。HPrP已经使用多种启动子表达，包括靶向表达至神经元的神经元特异性烯醇化酶启动子（NSE）、靶向表达至星形胶质细胞的GFAP特异性启动子和导致在许多组织中表达的天然启动子。这些类型的小鼠中的每一种都被培育成不表达小鼠PrP的PrP缺失小鼠。因此，我们有几种类型的小鼠，我们已经用来研究如何表达的PrP在特定的细胞类型影响羊瘙痒症的易感性，以及如何HPrP和小鼠PrP（MoPrP）相互作用。 在天然或NSE启动子控制下表达HPrP的小鼠在脑内接种后对仓鼠瘙痒症因子完全敏感。这一结果表明，PrP是至关重要的传输和表达仅限于神经元是足够的传输发生。如果NSE/HPrP在缺乏功能性MoPrP表达的小鼠中表达，则潜伏期缩短，表明MoPrP的存在以某种方式与HPrP竞争以延迟疾病的发作。这种效果对小鼠是保护性的，因为这种疾病要么被推迟，要么被完全避免。 在GFAP启动子控制下表达HPrP的小鼠（GFAP/HPrP）在接种仓鼠瘙痒症因子后没有临床上生病。然而，如果GFAP/HPrP在缺乏MoPrP的小鼠中表达，则它们在仓鼠试剂接种后确实生病。这一结果表明，星形胶质细胞特异性表达的HPrP也足以进行传递，尽管其效率远低于仅限于神经元表达的情况。此外，该结果证明了在表达MoPrP和HPrP的小鼠中MoPrP和HPrP之间的非常强的干扰。 因为TSE疾病被认为是经口传播的，我们还用仓鼠瘙痒症剂经口和腹膜内接种NSE/HPrP Tg小鼠和另一个命名为Tg 7的Tg系，其中HPrP在多个组织中表达。大多数通过这些途径接种的小鼠如果同时表达小鼠和HPrP则存活。这些结果表明，TSE疾病的治疗干预可以基于这些干预机制。 我们已经发现仓鼠瘙痒症病原体可以在小鼠体内持续存在，但不会引起临床疾病。（以前，小鼠被认为对仓鼠瘙痒症有抵抗力）。当将临床正常小鼠的脑或脾组织传递给仓鼠和其他小鼠时，仓鼠受体全部死亡。大多数小鼠在临床上表现良好，但其中几只小鼠的大脑中积累了与疾病相关的朊病毒蛋白，这表明小鼠适应性病原体正在形成。对仓鼠和小鼠的第三次传递显示仓鼠试剂仍然存在。此外，代表其中一个供体的小鼠在180天后出现临床疾病，表明一些小鼠适应品系正在进化。第四代也已完成，并显示了特定菌株进化的进一步证据。其中至少一种是仓鼠特异性的，另一种是小鼠特异性的，另外两种菌株对仓鼠和小鼠都是双嗜性的。这一数据表明，同样的过程可能发生在其他物种，并可能解释牛海绵状脑病的起源从羊瘙痒症。它还应该警告我们，同样的过程可能发生在美国的牛、羊和野生动物之间。

Transmissible spongiform encephalopathies(TSE)diseases affect a wide range of species including sheep,cattle, mink, humans, deer, elk and others. An issue of particular importance is to determine which TSE diseases can be transmitted to other species especially humans or livestock. To investigate the issue of cross-species transmission we used an animal model involving transmission of hamster scrapie agent to mice (prior to our study mice were considered resistant to hamster scrapie). We found that cross-species transmission between supposedly incompatible hosts can occur but involves a very slow but relentless process requiring several passages in the new host before finally emerging as a recognizable disease. This persistance and eventual adaptation suggests that similar situations could occur in other species combinations. In the USA there is concern that chronic wasting disease of deer and elk could be transmissible to humans or other species by similar mechanisms. To study this particular possibility we inoculated non-human primates with CWD infected brain. If the non-human primates become sick the possibility that humans might be susceptible would also seem possible. Several of the animals were inoculated approximately 26 months ago but have not shown any clinical evidence of TSE-like disease. Animals were inoculated by either the intracerebral or oral routes. In order to study other aspects of CWD we have developed mice transgenic for deer prion protein. Several lines have been derived that make deer PrPsen and after inoculation with CWD brain homogenates derived from CWD infected deer or elk develop clinical disease and disease-associated PrP-res. These mice are being used to study several aspects of CWD including pathogenesis in infected animals and whether persistence occurs in seemingly uninfected animals. They are also being used to develop assays for CWD infectivity found in naturally infected animals or animal models. Several other kinds of transgenic mice have been used over the past few years to investigate a variety of questions regarding the influence of prion protein on interspecies transmission, the role of specific cell types on TSE pathogenesis and kinetics of disease development. It is known that interspecies transmission can involve prion protein interactions between the prion proteins (PrP) of the species involved. To determine how PrP influences transmission among species we have developed mice transgenic for hamster prion protein (HPrP). The HPrP has been expressed using a variety of promoters including the neuron- specific enolase promoter (NSE) which targets expression to neurons, the GFAP specific promoter to target expression to astrocytes and natural promoters which result in expression in many tissues. Each of these types of mice has been bred to PrP null mice which do not express mouse PrP. Thus, we have available several types of mice which we have used to investigate how expression of PrP in specific cell types influences susceptibility to scrapie and how HPrP and mouse PrP (MoPrP) interact. Mice which express HPrP under the control of natural or NSE promoters are completely susceptible to hamster scrapie agent following intracerebral inoculation. This result showed that PrP is critical to transmission and that expression restricted to neurons is sufficient for transmission to occur. If NSE/HPrP was expressed in mice which lacked functional MoPrP expression, the incubation period was reduced indicating that the presence of MoPrP in some way competed with HPrP to delay the onset of disease. The effect was protective for the mice in that disease was either delayed or completely circumvented. Mice which express HPrP under the control of the GFAP promoter (GFAP/HPrP) did not become clinically sick after inoculation of hamster scrapie agent. However, if GFAP/HPrP was expressed in mice which lacked MoPrP, expression they did become sick following hamster agent inoculation. This result suggested that astrocyte specific expression oof HPrP was also sufficient for transmission to occur though much less efficiently than was true if expression was limited to neurons. Furthermore, this result demonstrated very strong interference between MoPrP and HPrP in the mice which expressed both. Because TSE diseases are thought to be transmitted orally we also inoculated the NSE/HPrP Tg mice and another Tg line designated Tg7, where HPrP is expressed in multiple tissues, with hamster scrapie agent orally and intraperitoneally. Most of the mice inoculated by these routes survived if they expressed both mouse and HPrP. These results suggested that therapeutic intervention in TSE diseases could be based on these interference mechanisms. We have found that hamster scrapie agent can persist in mice for the mouse's lifespan but not cause clinical disease. (Previously mice were thought to be resistant to hamster scrapie agent). When brain or spleen tissue from clinically normal mice was passed to hamsters and additional mice the hamster recipients all died. Most of the mice remained clinically well but disease-associated prion protein accumulated in the brains of several of them indicating that mouse-adapted agent was forming. A third pass to hamsters and mice showed that hamster agent was still present. In addition mice representing one of the donors developed clinical disease after 180 days showing that some mouse adapted strains were evolving. Fourth passages have also been accomplished and shows further evidence for the evolution of specific strains. At least one of these is hamster specific another mouse specific and two additional strains are dual tropic for hamsters as well as mice. This data suggests that the same process could occur in other species and may explain the origin of BSE from sheep scrapie. It also should warn us that the same process could occur in the USA between or among cattle, sheep and wildlife.