Role of avian macrophages in the pathogenesis of infectious bronchitis virus infection

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Poultry meat and eggs are important sources of protein in the Canadian diet. Canada's poultry industry has been valued at ~ $3.9 billion (2014), contributing 6.9% of cash receipts to farming operations in Canada with annual production of 663 million birds and >7 billion eggs. However, a major limitation of the poultry industry is morbidity and mortality associated with viruses that enter via the respiratory mucosa. For example, infectious bronchitis (IB) is a highly contagious respiratory viral infection, with global impacts (including substantial effects on North American chickens) on health, productivity and costs. Control of IB is focused on vaccines containing laboratory-attenuated viruses, but there are frequently IB outbreaks in vaccinated chickens. There are two reasons for this. Firstly, weakened vaccine virus becomes pathogenic after passage through the flock. Secondly, mutation of field IB virus (IBV) (against the pressure imposed by vaccination) to more virulent forms causes severe disease. Consequently, a novel approach to mitigate effects of this disease is urgently required. Interactions between the host and IBV, as well as mechanisms that lead to either virus clearance or disease progression in chickens, are poorly understood. As a first step, new knowledge regarding the complexity of host-virus interactions, particularly host responses elicited against IBV, is required.****To elucidate host-virus interactions, the initial focus will be on macrophages, cells known to have major roles in non-specific and specific host responses against viral infections in mammals. However, whether avian macrophages have roles in the disease progression of IB in chickens, as well as non-specific and specific host responses against IBV infection in chickens, has not been well characterized. Therefore, the roles of macrophages as well as the mediators produced by macrophages such as nitric oxide and interleukins in causing IB and/or conferring resistance against IB in chickens, will be studied.****The proposed studies will produce new knowledge regarding interactions between the host and IBV, and mechanisms that lead to virus clearance or disease development in chickens. Given the paucity of current knowledge in this area, the proposed studies are expected to provide novel insights into the role of macrophages in host responses and disease progression of IBV infection in chickens. The long-term goal of the proposed research is to provide a basis for immune intervention strategies for the control of IBV infection, which is prevalent in Canada and globally causing significant economic losses in poultry industry.****