Biomarkers of the innate immune response to disease in chickens: acute phase proteins and resistance to disease

The acute phase response is central to the innate host defence system against trauma, inflammation and infection and is composed of a wide range of systemic reactions including the production by the liver of acute phase proteins (APP) and secretion into the circulation. Little is known of the dynamics of the APP response in chickens, the prevalence of increased APP in production flocks the heritability of baseline or stimulated APP expression or the value to the industry of monitoring APP in chicken either as a tool for bird health or for breeding for disease resistance. This project will provide the groundwork to close these gaps in our knowledge. A limited number of investigations relating to APP in poultry have been reported and in chickens or turkeys serum amyloid A (SAA), ovotransferrin (oTFR), hemopexin (Hx) ceruloplasmin (Cp) and alpha-1 acid glycoprotein (AGP) have been shown to be positive major/moderate APP. Haptoglobin (Hp) or its equivalent in chicken blood, PIT 54, has also been identified as an APP while albumin is a negative APP as its concentrations falls during the APP response. A pilot study has shown changes in serum proteins changes in broilers culled due to bacteriological pathology. Complement C3 (CC3) was identified as a moderate chicken APP and Cp was confirmed as an APP in this species. The objective of this studentship is (1) to identify, characterise and quantify the pathophysiological responses of the chicken acute phase proteins and (2) to assess the relationship between the APP serum concentrations and genetic, phenotypic, nutritional and environmental factors related to production of healthy chicken. To achieve the first objective pooled serum from broilers with bacteriological pathology will provide the sample for confirmation by proteomic analysis of known APP and will also identify potential novel APP by comparison to serum proteome of healthy chickens. Methods, established in the Glasgow laboratory for purification of APP from other species will be adapted for purification of the chicken APP and antibody raised to allow immunoassay development. Immunoassays developed during the studentship will be validated by comparison to pathological investigation of individual broilers with bacterial pathology and other acute phase inducing conditions of inflammatory or traumatic causation. Non-hepatic synthesis of APP, which has been reported in other species, will be characterised by quantitative PCR using primers for identified APP. To achieve the second objective, serum samples will be collected, by Aviagen (contribution in kind) from growing meat chickens of approximately 6 weeks of age. Two distinctly different genetic lines of chickens will be studied. One line (Line A) is genetically relatively resistant to infection and one (Line B) is more susceptible. The chickens will be reared in 2 different environments. The first population will be in a high health status environment and feed will be supplied ad libitum. The second population will be reared in Aviagen's challenge environment which has been developed to mimic the lower quartile of UK broiler production facilities. Here the birds are exposed to a lower standard of nutrition, a greater level of environment disease challenge and exposed to more virulent commercial vaccines. Serum samples will be collected from 100 chickens in each group. A power calculation of the indicated that with n = 100, there is a 99% probability of detecting 3% of the difference between medians found in the pilot study for Cp and 10% of the difference found for CC3. Differences in APP that are suitable as biomarkers of disease would be detectable within this range. The health status of the chickens will be verified by Dr Barry Thorp of the St David Vet Practice who will check flock records and health history of the flocks. Post mortem examination will be performed on a subset of the birds in each environment.