Functional Genomics and Cellular Immunity to Salmonella

NON-TECHNICAL SUMMARY: The US poultry industry is a multibillion-dollar industry that annually loses 10 to 15% of its potential income due to disease. Additionally, pathogens that infect poultry can cause a major human health risk. Salmonella causes over one million cases of illness and about 500 deaths annually in the US. Understanding the identity, molecular variation, and functional associations of genes that control response to Salmonella will provide the necessary information for genetic enhancement of disease resistance in poultry. The improvements can be made by classical genetic selection techniques using the naturally occurring variation that exists in populations. Health can also be enhance by adding beneficial substances to the diet. The overall goal of this mission-linked project is to enhance host genetic resistance to Salmonella enteritidis (SE), so as to reduce bacterial burden in the live bird and thereby improve production efficiency and pre-harvest food safety. The results of this project are expected to be the identification of genes, biochemical pathways, and dietary factors that enable immune cells to control Salmonella burden in poultry, even in the face of stress. The application of the results in the poultry industry will have positive and lasting impact on the production of poultry and on food safety by providing novel, environmentally-friendly, non-antibiotic based strategies to knowledgeably use existing biodiversity to reduce microbial burdens in the live animal and in animal products. <P>APPROACH: The research for the three specific objectives will be conducted as described below. <OL> <LI> Baseline information about cytokines involved in regulation of chicken heterophil function will be collected, and three distinct genetic lines of chickens compared in order to delineate the potential role of different genes in innate defense mechanisms. Exposure of heterophils to different strains of common bacterial pathogens and comparative analysis of function and cytokine gene expression will provide information about genes involved in chicken innate defenses and how activation/suppression of different genes influences heterophil function during interaction with bacterial pathogens. <LI> Genetically different chicken lines will be exposed to dietary corticosteroids to simulate stress and dietary immunomodulators (ascorbic acid, â-glucan), and heterophil function will be evaluated along with cytokine gene expression profiles. Suppression and activation of heterophil function will be compared with differences in cytokine expression, and candidate genes that participate in modulation of innate immune response of chickens will be determined. Advanced intercross line resource populations will be comprehensively screened for genomic variation closely linked to genes controlling functional traits. <LI> Chicken lines will be challenged with two strains of S. enteritidis and heterophil function, cytokine expression profile and pathology will be monitored. Examined parameters will be compared to determine genes that participate in innate defense mechanisms and disease resistance. </OL><P>
PROGRESS: 2007/02 TO 2008/01 <BR>
OUTPUTS: Several experiments were conducted to optimize protocols in this newly established project. Experimental populations of chickens were produced from three unique inbred lines and from advanced intercross lines, the F13 generation. From a small-scale study, protocols were optimized for blood sample collection and laboratory procedures for heterophil isolation and assessment of functional activity, as well as RNA isolation from isolated heterophils and determination of cytokine gene expression. From a large-scale study, samples were collected and phenotypic data recorded on chickens that either were or were not direct-fed dietary microbial products for potential immune enhancement. Results were disseminated locally through oral reports to faculty and student groups. Two Ph.D. students received instruction and research experience through participation in the project. <BR>PARTICIPANTS: Project directors were Susan J. Lamont, Dusan Palic and Claire Andreasen. Participants from Iowa State University were: Dr. Phongsakorn Chuammitri, veterinarian and Ph.D. graduate student (developed methodology for investigations of heterophil extracellular traps or HETs in chickens) and Sarah Beth Redmond, Ph.D. graduate student and USDA National Needs Fellow (collection of samples from chickens, coordination of live-bird trials, analysis of data on animal phenotypes, isolation and quality characterization of RNA from samples for future assays of gene expression, preparation of presentation). <BR>TARGET AUDIENCES: Veterinarians, nutritionists, scientists in poultry breeding and genetics, commercial breeders of poultry. <P>
IMPACT: 2007/02 TO 2008/01
<BR>The optimization of protocols for collection and assessment of avian heterophil activity and gene expression will allow effective and valid studies to take place in the future investigating more treatment effects and greater numbers of birds. The identification of avian heterophil extracellular traps (HETS) fills an essential gap in comparative genomic information of innate immune defenses, and helps to explain the biological activity that avian heterophils may use to effectively protect against bacterial disease. Observed differences in heterophil function in three chicken lines indicated that changes in genetic traits of these lines may be involved in variability of the host defense mechanisms against bacterial pathogens. Collection of phenotypic data and biological samples from birds fed different dietary treatments provide the materials and information needed for assessment of dietary treatment and genetics on heterophil function and gene expression. The funded project allowed the establishment of a productive new team of researchers combining expertise in poultry genetics, microbiology, immunology and veterinary medicine.