Impact of T lymphocytes on clinical disease, immune responses and transmission of bluetongue virus in sheep

库蠓传播的病毒在全世界的反刍动物中引起重要的经济疾病。目前，其中最重要的是蓝舌病病毒（BTV），在过去的十年里，它仅在西北欧就造成了超过10亿欧元的损失。该病毒对英国反刍动物生产构成持续威胁，2015年在法国再次出现的血清8型毒株凸显了这一威胁。感染BTV通常会在绵羊中引起严重疾病，尽管牛的临床疾病较轻，但对生产参数的不利影响在经济上具有破坏性。受感染的动物恢复后可免受BTV再次感染，但仅限于相同血清型的毒株。同样，商业疫苗也可以获得，但只能防止同一血清型的再次感染。迄今为止，已发现至少27种BTV血清型，这些血清型的全球分布在不断变化。尽管疫苗接种成功地在2008年消灭了英国和北欧的一种毒力强的BTV-8毒株，但BTV的多血清型性质对控制该病毒构成了一个重大问题。设计针对多种BTV血清型提供交叉保护的新疫苗需要详细了解导致受感染动物清除病毒的免疫反应机制。然而，我们对这些抗btv免疫反应的了解仍然很肤浅。在这个项目中，我们将探索一种关键细胞类型（T淋巴细胞也称为T细胞）的作用，它是抗病毒免疫反应的核心，要么使其他细胞产生抗病毒抗体，要么直接消除病毒感染的细胞。T细胞出现在不同的亚群中，但到目前为止，亚群在对BTV的免疫反应中的具体贡献尚不清楚。此外，已知T细胞亚群本身也可以被BTV感染。然而，目前尚不清楚这些T细胞亚群的感染在多大程度上导致了BTV感染动物中检测到的大量病毒。我们发现的一个关键观察结果是，库蠓的血液喂养导致大量T细胞（以及其他细胞）聚集到咬伤部位。因此，T细胞也有可能影响病毒在昆虫载体之间的传播。在受控的实验条件下，现实地检查天然哺乳动物宿主、昆虫媒介和病毒之间的复杂相互作用是具有挑战性的，而且大多数实验研究都受到用针将病毒接种到宿主和/或使用啮齿动物等模式宿主物种的影响。在本项目中，我们将直接研究T细胞在BTV天然宿主羊体内的作用，并利用感染的蠓传播BTV。通过给绵羊接种抗体来去除特定的T细胞亚群，我们可以开展揭示每个亚群在BTV免疫应答中的重要性的研究。我们将探讨的关键领域包括是否产生更多或更少的BTV，以及临床疾病是否因缺乏特定的T细胞亚群而不同。我们还将测量抗BTV抗体和抗病毒细胞因子的产生，以及剩余T细胞识别BTV成分的潜力。此外，未感染的库蠓将被允许以感染BTV的绵羊为食，以便对病毒传播进行检查。还将比较治疗组和对照组之间的细胞数量和对这些叮咬的蠓吸血反应的皮肤炎症。这项全面的BTV绵羊感染研究将为T细胞亚群在BTV产生、抗BTV免疫反应、临床后果和病毒传播中的特定作用提供急需的数据。虽然获得的结果对于推进BTV的治疗和控制将特别重要，但我们使用自然传播系统可能会加深对这一与其他虫媒病毒相关的过程的理解。

Viruses transmitted by Culicoides biting midges cause economically important diseases in ruminants worldwide. Currently, the most important of these is bluetongue virus (BTV), which has inflicted over 1000m Euros of damage in North-West Europe alone during the past decade. This virus represents an ongoing threat to UK ruminant production, highlighted by re-emergence of a serotype 8 strain in France during 2015. Infection with BTV often causes severe disease in sheep and although clinical disease is milder in cattle, adverse effects on production parameters are economically damaging. Infected animals which recover are protected from BTV re-infection, but only by strains of the same serotype. Similarly, commercial vaccines are available but only protect against re-infection by the same serotype. To date, at least 27 serotypes of BTV have been detected and the global distribution of these constantly changes. Although vaccination successfully led to the eradication of a virulent BTV-8 strain from the UK and Northern Europe in 2008, the multiple serotype nature of BTV presents a major problem to control of the virus.Designing new vaccines that provide cross-protection against multiple BTV serotypes requires a detailed understanding of the immune response mechanisms that result in virus clearance from infected animals. However, our knowledge of these anti-BTV immune responses remains superficial. In this project we will explore the role of a key cell type (T lymphocytes also called T cells) that is central to the anti-viral immune response, either by enabling other cells to produce anti-viral antibodies, or by directly eliminating virus infected cells. T cells occur in different subsets, but so far the specific contribution of subsets in the immune response to BTV is unknown. Additionally, it is known that T cell subsets can become infected with BTV themselves. However , it is unclear how much infection of these T cell subsets contributes to the high amounts of virus detected in BTV infected animals. A key observation we have shown is that blood-feeding of Culicoides leads to the recruitment of high numbers of T cells (among other cells) to the biting sites. Hence, T cells also have the potential to influence virus transmission from and to the insect vector. It is challenging to realistically examine complex interactions between natural mammalian hosts, insect vectors and viruses under controlled experimental conditions and most experimental studies are compromised by either needle-inoculating the virus into the host and/or the use of model host species such as rodents. In this project we will study the role of T cells directly in sheep, a natural host for BTV and carry out transmission of BTV using infected biting midges. By inoculating sheep with antibodies to remove specific T cell subsets we can conduct studies revealing the importance of each subset in the immune response to BTV. Key areas we will explore include whether more or less BTV is produced and whether clinical disease differs according to the absence of a specific T cell subset. We will also measure the production of anti-BTV antibodies and anti-viral cytokines, alongside the potential for the remaining T cells to recognise BTV components. In addition, uninfected Culicoides will be allowed to blood-feed on BTV infected sheep enabling virus transmission to be examined. Cell populations and skin inflammation in response to blood-feeding of these biting midges will also be compared between treatment and control groups.This comprehensive BTV sheep infection study will provide much needed data on the specific role of T cell subsets on BTV production, anti-BTV immune responses, clinical consequences and virus transmission. While the results obtained will be particularly important to advance BTV treatment and control, our use of a natural system of transmission is likely to yield an enhanced understanding of this process that is relevant to other arboviruses.