1. Institute for Animal Health, Compton, Berkshire, United Kingdom.
2. Ibrahim Eldaghayes and Lisa Rothwell contributed equally to this work.
3. Present address: Centre for Molecular Microbiology and Infection, Department of Biological Sciences, Imperial College, London, United Kingdom.
4. Present address: Autoimmunity Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Insitutes of Health, Bethesda, Maryland.