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重要组成部分。如果没有这些疫苗，鸡将在幼年时死于感染，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，在全世界的鸡中引起严重的疾病暴发；由于体重增加和质量问题，它影响了肉禽的全球生产，并通过减少所产蛋的数量和质量影响了蛋的生产。目前已有针对IBV的有效且经济可行的疫苗，但由于针对不同IBV毒株的交叉保护水平不足，因此需要将现有疫苗进行多种组合。交叉保护不良是病毒主要表面蛋白（刺突(S)蛋白）变异的结果。具有S蛋白差异的IBV新变异株在田间经常出现，通过基于S蛋白序列的分析，无法预测哪些疫苗将诱导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试验才能阐明需要哪种疫苗组合来预防新的IBV菌株。这一提议将解决该病毒看似不可预测的性质。IBV独特的反向遗传系统的可用性有可能导致新一代活疫苗的开发。在这个提议中，我们将产生与经济上最重要的IBV菌株（M41, 4/91和QX）相同的重组病毒，除了免疫优势的S1亚基。用相同病毒和不同病毒进行的疫苗挑战实验将确定是否存在不同程度的保护。交叉防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菌株S1亚基上的关键区域或表位，这些区域或表位负责诱导保护性免疫反应。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）。在接种单株或多株IBV疫苗后，鉴定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，我们将进一步了解鸟类对病毒的免疫反应压力如何驱动病毒改变或突变。这将涉及IBV菌株在鸡蛋中的传递，与疫苗的生产方式相同。然而，病毒的复制会受到添加针对该病毒的抗体的免疫压力。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，但没有在鸟类中进行测试。利用现代深度测序技术，我们将确定由于免疫压力和病毒能够逃避应用疫苗的过程而发生的分子变化，这些变化可能演变成一种新的变体。通过了解和操纵疫苗接种后控制病毒适应的过程，我们的目标是确定减少疫苗毒株变化和引起破坏性疾病暴发的危险的方法。该提案的结果将提供(1)关于为什么用于控制重要的禽类地方性病原体IBV的疫苗不能引起交叉保护的关键信息，(2)关于有效使用现有疫苗的信息，(3)开发更有效的疫苗，从而确保家禽养殖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.