Effects of Nod-like receptor activity on protective immunity against Salmonella infection

Infectious diseases remain major problems with significant economic and social impact despite the availability of antimicrobials and vaccines. The development of resistance to antimicrobials by microorganisms means that alternative control measures are required. Control of food-borne bacterial infections that infect people is particularly challenging because some bacteria can live in livestock without causing any harmful effects under the right circumstances (for example species of Salmonella enterica or Campylobacter in chickens) yet cause disease in humans. How this species-specific bacterial "tolerance" occurs is not understood which makes design of control strategies difficult. Vaccination strategies have reduced disease incidence for some bacteria, but many current vaccines are not ideal. Alternative approaches to combat infectious disease in livestock are to use selective breeding for disease resistance or to generate genetically modified animals to alter their susceptibility to infection. To design suitable control strategies it is essential to understand how bacteria co-exist with livestock.
Bacteria are recognised in humans and animals by specialised proteins called pattern recognition receptors (PRRs) to activate anti-bacterial immunity. There are major differences in the repertoires of PRRs and in the bacteria they detect between different species of mammals and birds. Our previous BBSRC funded research has found that some of the PRRs specifically the Nod Like Receptors (NLRs) NLRC4 and Nod2, that are missing from chickens, are important regulators of immune responses against Salmonella. Using comparative studies between mouse and chicken cells this grant will identify the NLR-signalling pathways driving the host response to infection. By expressing human NLRC4 or Nod2 in chicken cells and in chickens we will determine whether these PRRs contribute to why humans and animals react differently to the same salmonellae.

Infectious diseases remain major problems with significant economic and social impact despite the availability of antimicrobials and vaccines. The development of resistance to antimicrobials by microorganisms means that alternative control measures are required. Control of food-borne zoonotic bacterial infections is particularly challenging because some bacteria can behave like commensals in livestock under the right circumstances (for example Salmonella species) yet are pathogens in humans. The molecular basis for this species-specific bacterial "tolerance" is not understood which makes design of control strategies difficult. Vaccination strategies have reduced disease incidence for some bacteria, but many current vaccines have been generated empirically which often results in a product with limited efficacy. Alternative approaches to combat infectious disease in livestock are to use selective breeding for disease resistance traits or to generate genetically modified animals to alter their susceptibility to infection. To design suitable control strategies it is essential to determine how pathogens interface with host immunity

Pathogen recognition by host pattern recognition receptors (PRRs) activates innate and adaptive immunity. There are major differences in the repertoires of PRRs and in how they respond to ligands between different species of mammals and birds. The Nucleotide Oligomerisation Domain (Nod)-like receptors (NLRs) show wide species differences in repertoire with mice having 30, humans 22, and chickens 7. Our data show that the NLRs NLRC4 and Nod2 that are missing from chickens are important regulators of TH1 immunity against Salmonella infection. Using comparative studies between mouse and chicken cells this research will identify the NLR-signaling pathways driving the host response to infection. By expressing human NLRC4 or Nod2 in chickens we will determine whether these PRRs contribute to species-specific host responses to salmonellae.

A central part of any strategy to reduce diseases such as salmonellosis must be intervention to induce the immune system to prevent infection or to clear infection rapidly. This is currently achieved by vaccination or immunotherapy. Alternative strategies include breeding animals for disease resistance traits or transgenic expression of genes to enhance bacterial clearance. To generate new vaccines, improve current vaccines or to pursue genetic modification we must understand the mechanisms by which immunity is induced, and this research will provide an essential element of that knowledge.
Impact will be delivered to beneficiaries in the commercial private sector and in the wider public sector. This grant proposal is supported by an IPA agreement with Pfizer because the project will generate information that can be used to inform rational vaccine development against salmonellosis and potentially other bacterial pathogens (by 36 months). The grant is also likely to generate information as to which receptors are important for recognising salmonellae in species of commercial importance i.e. chickens (by 24 months). An added benefit of this grant is that the Nod-like receptors that are activated by salmonellae in mice are also conserved in humans: therefore this grant will generate data which may improve human vaccines against salmonellosis and will be of interest to the medical pharmaceutical industry (by 24 months). Development of improved vaccines and vaccine strategies will enhance UK economic competitiveness in animal and medical heath programs. The grant will have impact on the wider public sector by continuing our program of scientific communication. Our laboratories hosts up to 6 school children a year on work placements to engage them in the fundamentals of scientific research. Our research work is communicated in public forums such as the Cambridge science fair and during open days at the veterinary school. Dr Bryant is working closely with Dr Chris Smith of BBC Radio Cambridgeshire's Naked Scientists program to feature work on zoonotic diseases, with an emphasis on bacterial pathogens, and on multidisciplinary research (http://www.thenakedscientists.com/HTML/podcasts/show/2010.07.11/). The research in this grant will contribute to the zoonosis interest of the radio program and this should be realised within 24 months of starting the project. The grant will contribute to influencing policy decisions via Professor Maskell's membership of the General Advisory Committee on Science (GACS) at the Food Standards Agency and Dr Bryant's membership of the Veterinary Products Committee of the Veterinary Medicines Directorate. This project will develop new technical skills for the two postdoctoral researcher associates (PDRAs). Dr Tourlomousis will learn in vitro cell culture techniques to complement his skills in in vivo biology. The second, junior PDRA will use a range of skills including molecular techniques and in vitro cell culture skills and will receive training in these areas. Both PDRAs will learn imaging techniques through Dr Bryant's on-going collaboration with Dr Cicuta in Physics which forms part of her BBSRC Research Development fellowship. Both PDRAs will be involved in the public communication activities of this project. PDRAs will also attend BBSRC media training courses and University-run workshops on grant writing, communication skills and software training to develop their transferrable skills.