Towards control of Infectious bronchitis virus; understanding cross-protection and the genetic plasticity of IBV

针对众多地方性病原体的疫苗接种是家禽业的一个重要组成部分。如果没有这些疫苗，鸡将在早期死于感染，使该行业的生产率远远低于可持续水平。传染性支气管炎病毒(IBV)是一种地方性病毒，在世界范围内引起严重的疾病暴发；由于体重增加和质量问题，它会影响全球肉类禽类的生产，并通过减少鸡蛋生产的数量和质量来影响鸡蛋生产。针对IBV的有效且经济可行的疫苗是可用的，但由于针对不同IBV毒株的交叉保护水平不够，因此需要多种可用的疫苗组合。较差的交叉保护是病毒的一种主要表面蛋白(尖峰蛋白(S))发生变异的结果。现场经常出现S蛋白不同的新的IBV变异株，通过基于S蛋白序列的分析，无法预测哪种疫苗将对新出现的病毒产生保护作用。只有在鸡身上进行复杂而昂贵的测试才能阐明需要哪种疫苗组合来预防新的IBV毒株。这项建议将解决该病毒似乎不可预测的性质。IBV独特的反向遗传学系统的可获得性有可能导致新一代活疫苗的开发。在这项提议中，我们将产生与经济上最重要的IBV毒株(M41、4/91和QX)相同的重组病毒，除了免疫优势的S1亚基。疫苗接种-用相同和不同病毒进行的挑战实验将确定是否存在不同程度的保护。交叉保护水平不足和不可预测的原因是本研究的主要重点。最终，我们将确定经济上最重要的IBV毒株S1亚单位上负责诱导保护性免疫反应的关键区域或表位。我们将使用新的“表位指纹”技术来确定疫苗接种后诱导的抗体识别的关键区域(表位)。在用单个或多个IBV毒株接种疫苗后识别关键区域将使我们能够确定疫苗需要哪些表位来诱导保护。当新的病毒株出现时，我们将能够预测需要哪些疫苗来诱导对新病毒株的有效保护。此外，我们还将进一步加深我们对鸟类免疫反应对病毒的压力如何促使病毒发生变化或变异的理解。这将涉及IBV毒株在鸡蛋中的传递，这与疫苗生产的方式相同。然而，由于增加了针对该病毒的特异性抗体，病毒的复制将受到免疫压力。这将基本上模拟对复制病毒施加的免疫压力，就像接种疫苗后自然发生的那样，但没有在禽类身上进行测试。使用当代的深度测序技术，我们将识别由于免疫压力而发生的分子变化，以及病毒能够逃避所应用的疫苗的过程，从而有可能进化成新的变种。通过了解和控制疫苗接种后控制病毒适应的过程，我们旨在确定降低疫苗株变化和引起破坏性疾病爆发的危险的方法。这项建议的结果将提供(1)用于控制重要的禽类地方性病原体IBV的疫苗为何未能诱导交叉保护的关键信息，(2)有效利用现有疫苗的信息，以及(3)更有效的疫苗的开发，从而确保家禽养殖业不仅是一个安全的食物来源，而且还增加了英国的经济竞争力。

Vaccination against numerous endemic pathogens is an essential component of the poultry industry. Without these vaccines chickens would succumb to infection at an early age, reducing the productivity of the industry well below sustainable levels. Infectious bronchitis virus (IBV) is an endemic virus that causes severe disease outbreaks in chickens worldwide; it affects the global production of meat-type birds, due to problems in weight gain and quality, and egg production through decreasing the numbers and quality of eggs produced. Effective and economically viable vaccines against IBV are available, but multiple combinations of available vaccines are needed because the level of cross-protection against different IBV strains is insufficient. Poor cross-protection is the result of variation in a major surface protein of the virus (the spike (S) protein). New variant strains of IBV with differences in the S protein appear regularly in the field and, through analysis based on the sequence of the S protein, it is impossible to predict which vaccines will induce protection against the newly emerged viruses. Only elaborate and expensive testing in chickens elucidates which vaccine combination is needed to protect against a new strain of IBV.This proposal will address the seemingly unpredictable nature of the virus. The availability of a unique reverse genetics system for IBV has the potential to lead to the development of a new generation of live vaccines. In this proposal we will generate recombinant viruses that are identical, except for the immunodominant S1 subunit, of the economically most important IBV strains (M41, 4/91 and QX). Vaccination-challenge experiments with the same and with different viruses will identify if there are different degrees of protection. The causes of insufficient and unpredictable levels of cross-protection are the main focus of this study. Ultimately we will determine the key regions or epitopes on the S1 subunit of the economically most important IBV strains that are responsible for inducing protective immune responses. We will use novel "epitope fingerprinting" technology to determine the key regions (epitopes) that are recognised by the antibodies induced after vaccination. Identification of key regions following vaccination with a single IBV strain or multiple strains will allow us to determine which epitopes are needed by a vaccine to induce protection. When new virus strains emerge we will then be able to predict which vaccines will be required to induce effective protection against the new virus strain.Moreover, we will further develop our understanding of how pressure from the bird's immune responses on the virus might drive the virus to change or mutate. This will involve the passage of an IBV strain in eggs, in the same way as vaccines are produced. However, the replication of the virus will be put under immune pressure by the addition of antibodies specific for this virus. This will essentially mimic the immune pressure applied to the replicating virus, as occurs naturally after vaccination but without testing this in birds. Using contemporary deep sequencing technology we will identify the molecular changes that occur as a result of immune pressure and the process by which the virus is able to evade the applied vaccine, potentially evolving into a new variant. By understanding and manipulating the processes that govern virus adaptation after vaccination, we aim to identify ways of reducing the danger of vaccine strains changing and causing damaging disease outbreaks.Results from this proposal will provide (1) crucial information on why vaccines used to control an important avian endemic pathogen IBV fail to induce cross-protection, (2) information for the efficient use of existing vaccines and (3) the development of more efficient vaccines, thus ensuring that poultry farming remains not only a secure food source but also increases the economic competitiveness of the UK.