Immunobiology Of Scrapie Virus Infection

传染性海绵状脑病(TSE)影响的物种范围很广，包括羊、牛、水貂、人、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，特别是人或牲畜。为了研究跨物种传播的问题，我们使用了一个动物模型，该模型涉及将仓鼠瘙痒病病原体传播给小鼠(在我们的研究之前，小鼠被认为对仓鼠瘙痒病具有抵抗力)。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，需要在新宿主中传代几次，才能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，类似的情况也可能发生在其他物种的组合中。 在美国，人们担心鹿和麋鹿的慢性消耗性疾病可能会通过类似的机制传播给人类或其他物种。为了研究这种特殊的可能性，我们给非人类灵长类动物接种了CWD感染的大脑。如果非人类灵长类动物生病，人类可能也会受到影响。其中几只动物大约在18个月前接种了疫苗，但没有表现出任何类似TSE疾病的临床证据。为了研究CWD的其他方面，我们建立了鹿普恩蛋白转基因小鼠。已经衍生出几条线，似乎构成了适当类型的PrP。我们正在确定小鼠的特征，以便它们可以用于各种旨在确定CWD发病机制的研究。 在过去的几年里，一些其他类型的转基因小鼠被用来研究各种问题，如Pron蛋白对物种间传播的影响，特定细胞类型在TSE发病机制中的作用以及疾病发展的动力学。已知的是，物种间的传播可能涉及到所涉及物种的PrP之间的PrP蛋白相互作用。为了确定PrP如何影响物种间的传播，我们培育了转仓鼠PrP蛋白(HPRP)的小鼠。HPRP的表达有多种启动子，包括神经元特异性的烯醇化酶启动子(NSE)，星形胶质细胞的GFAP特异性启动子，以及在许多组织中导致表达的天然启动子。这些类型的小鼠中的每一种都被培育成PrP缺失的小鼠，这些小鼠不表达小鼠PrP。因此，我们有几种类型的小鼠，我们已经用来研究PrP在特定细胞类型中的表达如何影响对瘙痒病的敏感性，以及HPRP和小鼠PrP(MoPrP)是如何相互作用的。 在自然启动子或NSE启动子控制下表达HPRP的小鼠在脑内接种后对仓鼠瘙痒病完全敏感。这一结果表明PrP对传递至关重要，仅限于神经元的表达就足以进行传递。如果在缺乏MoPrP功能表达的小鼠中表达NSE/HPRP，潜伏期就会缩短，这表明MoPrP的存在在某种程度上与HPRP竞争，从而延迟了疾病的发生。这种效果是对小鼠的保护作用，因为这种疾病要么被推迟，要么完全被绕过。 在GFAP启动子(GFAP/HPRP)控制下表达HPRP的小鼠在接种仓鼠瘙痒病制剂后没有出现临床疾病。然而，如果GFAP/HPRP在缺乏MoPrP表达的小鼠中表达，那么它们在接种仓鼠制剂后确实会生病。这一结果表明，星形胶质细胞特异性表达HPRP也足以进行传递，尽管比仅限于神经元表达的效率要低得多。此外，在表达MoPrP和HPRP的小鼠中，这一结果表明MoPrP和HPRP之间存在非常强的干扰。 由于TSE疾病被认为是通过口服传播的，我们还将HPRP在多个组织中表达的另一个TG系Tg7和NSE/HPRP TG小鼠接种到仓鼠瘙痒病疫苗的口服和腹腔注射中。通过这些途径接种的小鼠，如果同时表达小鼠和HPRP，大多数都能存活下来。这些结果表明，对TSE疾病的治疗干预可能基于这些干扰机制。 我们已经发现，仓鼠瘙痒病制剂可以在小鼠体内持续存在，但不会导致临床疾病。(以前，老鼠被认为对仓鼠瘙痒病具有抵抗力)。当来自临床正常小鼠的脑或脾组织被转移给仓鼠和其他小鼠时，接受移植的仓鼠全部死亡。大多数小鼠的临床表现良好，但其中几只小鼠的大脑中积累了与疾病相关的Pron蛋白，这表明正在形成小鼠适应的因子。对仓鼠和老鼠的第三次测试表明，仓鼠制剂仍然存在。此外，代表其中一名捐赠者的小鼠在180天后出现临床疾病，表明一些小鼠适应的品系正在进化。第四代也已经完成，并为特定菌株的进化提供了进一步的证据。其中至少有一种是仓鼠特有的，另一种是小鼠特有的，另外两种菌株对仓鼠和小鼠都是双向性的。这一数据表明，同样的过程也可能发生在其他物种中，并可能解释绵羊瘙痒病的起源。它还应该警告我们，同样的过程可能会在美国发生在牛、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 18 months ago but have not shown any clinical evidence of TSE-like disease. In order to study other aspects of CWD we have developed mice transgenic for deer prion protein. Several lines have been derived that appear to make the appropriate kind of PrP. We are in the process of characterizing the mice so that they can be used for a variety of studies aimed at defining CWD pathogenesis. 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 of 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.