ANIHWA call2: Understanding mucosal immunology and co-infections in the chicken to drive vaccine strategies

Despite the fact that vaccine use in poultry is greater than in any other farmed species, the mechanisms by which they induce protection, particularly at mucosal surfaces, are poorly understood. Many diseases constraining avian productivity and welfare affect the respiratory tract and are multi-factorial. A better understanding of responses in the respiratory tract to bacterial and viral infections, co-infections and vaccines is needed to control endemic production diseases.

Avian pathogenic Escherichia coli (APEC) cause severe respiratory and systemic disease, threatening food security and avian welfare at a time of increasing global demand. Infections frequently involve sepsis, inflammation of internal organs and reduced egg yield/quality, with losses through early mortality, reduced productivity and product condemnation. The expansion of free-range production systems will increase the incidence of colibacillosis through greater exposure of birds to environmental pathogens, stress and injury associated with forming a social hierarchy. Importantly, APEC infections are frequently associated with respiratory viral infections.

The nature and consequences of host-pathogen interactions during APEC (co-)infections are poorly understood. Virulence factors of APEC, antagonistic or synergistic effects of co-infection and the basis of immunity and resistance are ill-defined. The EC-wide ban on prophylactic antibiotic use and transmissible resistance render poultry susceptible to APEC infection. Existing vaccines confer limited protection. This project will advance understanding of mucosal immune responses in the avian respiratory tract. It will provide a comprehensive description of the respiratory tract immune system, leading to new tools to study immune responses and improved understanding of the mechanism and site of antigen presentation in the lung. We will thereby identify correlates of resistance and susceptibility to, and the impact of viral infections on the outcome of, APEC infection. Using transgenic chickens we will further characterise the role of antigen-presenting cells and humoral immunity during APEC infection and vaccination, for example by using our unique MacRed chickens (in which all cells of the mononuclear phagocyte lineage (macrophages, monocytes and dendritic cells) express a fluorescent protein driven by the chicken CSF-1 receptor), and immunoglobulin knock-out chickens (which lack the B cell receptor and thus antibody).

Chickens are the most heavily vaccinated of farmed animal species yet the sites and mechanisms of antigen presentation are poorly understood. Our ability to rationally modulate the mucosal immune response to vaccination in birds is limited by this lack of knowledge. The overall aim of the proposed project is to improve understanding of protective immunity in the chicken, particularly during viral and bacterial co-infections of the respiratory tract, to improve control of endemic production diseases. We will use cutting-edge technologies, particularly our unique inbred and transgenic chickens, to investigate the role of antigen-presenting cells (APCs) and B cells in the mucosal immune response in the respiratory tract. We will exploit this knowledge to explore ways of modulating the avian mucosal immune response to improve magnitude, duration and cross-protective efficacy of vaccine-induced responses.

Our specific aims are to:
1) Understand the mucosal immune response of the respiratory tract.
2) Identify immune responses that correlate with resistance and susceptibility to avian pathogenic E. coli (APEC) infection.
3) Determine the role of APCs and humoral (B cell-mediated) immunity in APEC infection and vaccination.
4) Determine the effect of infectious bronchitis virus (IBV) co-infection on the outcome of APEC infection.
5) Determine the effect of low pathogenicity avian influenza virus (LPAIV) co-infection on the outcome of APEC infection.

The work proposed has direct relevance to the strategic priorities of the BBSRC, in particular those relating to animal health and food security. Infectious diseases are a constant threat to the poultry industry through losses or reduction in production, decreases in egg production and quality, and effects on animal welfare. Vaccines are used to control the major diseases of poultry but the immunological mechanisms that lead to success or failure of novel and current vaccines have not been elucidated and improvement has been hampered by the lack of fundamental knowledge of the chicken's mucosal immune system. The ability to combat infectious diseases which reduce the health and welfare of farm animals requires more efficient vaccines, reagents and functional assays to assess immune function and the need to understand host pathogen interactions at mucosal surfaces in the chicken. Outcomes of this work will provide crucial information for the development of more efficient vaccines, ensuring that poultry farming remains not only a secure food source but also increases the economic competitiveness of the UK.

The following stakeholders have been identified as beneficiaries of this work:

The poultry production industry
Infectious diseases cost the UK poultry industry billions of pounds per annum. Understanding vaccine responsiveness and resistance to diseases in poultry improves the efficiency of the industry, through improved protection against diseases and the development of more efficient vaccines.

The poultry breeding industry
The consequences of improved vaccine responses and disease resistance may provide a panel of phenotypic biomarkers which could be developed as affordable tools to inform breeding strategy. We have established collaborations with major poultry breeding companies.

The animal health industry
The RI has established collaborations, including direct support, with several vaccine companies that have resulted in ongoing assessment of potential vaccine candidates and immunomodulatory products. The data generated during this project will allow us to improve vaccine targeting and will develop tools to modulate immune responses at mucosal surfaces.

Animal welfare
The reduction of disease as a result of improved vaccine strategies supports the Five Freedoms implicit to animal welfare as set out by the Farm Animal Welfare Council.

General public and the environment
The consequences of improved vaccine responses and disease resistance will lead to a reduction in the prophylactic use of antimicrobials and the risk of contamination of the food chain and the environment. The world's chicken flock is now estimated to be around 21 billion, producing 1.1 trillion eggs and 60 billion broilers every year. Advances in the efficacy of poultry vaccines therefore have enormous potential to reduce animal suffering, improve the sustainability of agriculture and drive societal and economic prosperity.

Academia and Training
The multidisciplinary nature of this project will provide opportunities for broad training to all staff including other members and students of the institution ('strengthen the research community in the areas of disease and pest resistance of farmed animals through interdisciplinary research and the provision of training'). Results with respect to the identification of cell subsets associated with antigen uptake, processing and presentation will be of interest to a wide scientific community and will be published in peer-reviewed journals and presented at national and international scientific meetings.