Mucosal T cell defence in large animal models of infection

The study of cellular immune responses in the mucosa has proven difficult within humans. Capturing the respiratory mucosal immune response is challenging without invasive sampling methods; therefore, research in this area has leant heavily on the use of animal models. Livestock species are naturally infected by a range of diseases which are also major human public health concerns, including influenza in pigs, tuberculosis in cattle and lung disease in sheep. Influenza virus is estimated to cause 1 billion human infections annually with approximately 3- 5 million cases of severe illness and 300-500,000 deaths per year. Pigs make an ideal model for the study of influenza infection as they have comparable size and respiratory anatomy to humans and influenza strains such as the 2009 pandemic H1N1 are endemic in both humans and pigs. The T cell response to influenza has come under renewed investigation in recent years with the potential to target cross reactive T cell epitopes to multiple influenza strains. Additionally, innate like T cells, such as mucosal associated invariant T (MAIT) cells, a prominent T cell population in humans, are being increasingly studied for their role in influenza infection. Here, the kinetic of virus infection and T cell response to H1N1pdm09 influenza is investigated in inbred Babraham pigs and compared to commercial outbred animals. High level of nasal virus shedding continued up to day 4-5 post infection followed by a steep decline and clearance of virus by day 9. The T cell response developed from day 5-6 post infection reaching a peak at 9-14 days. BAL contained the most highly activated CD8 and CD4 T cells actively producing pro-inflammatory cytokines, which likely contribute to the elimination of the virus. The weak response in peripheral blood T cells did not reflect the robust local immune responses. The immune responses in the Babraham pig were comparable to outbred pigs, validating the Babraham pig as a model for pig immunology. Furthermore, new H1N1pdm09 influenza immunodominant T cell epitopes are described in the Babraham pig which will aid in future studies involving this animal model. Putative MAIT cells have been previously identified in pigs, cattle and sheep by qPCR-based methods though no MAIT cells have been phenotypically described in these species. In this study the MAIT cell population in pigs, cattle and sheep is determined using a variety of methods including functional activation assays and phenotypic assessment utilising species specific and xenogenic tetramers. In pigs the MAIT cell population was at the limits of detection. The absence of MAIT cells identified in pigs precluded the study of MAIT cells in the context of the influenza challenge studies. However, MAIT cells were identified in sheep and cattle and a detailed characterization was therefore performed in cattle. MAIT cells in cattle were highly phenotypically and functionally comparable to MAIT cells described in humans and mice and are activated by disease causing bacteria in vitro and in vivo. These data and techniques expand the understanding of the T cell response to influenza in pigs, support the use of the Babraham pig as a model for influenza research and enables cattle and sheep to be included as useful models for the study of MAIT cells in these species.