The goal of this project is to identify parameters of the immune response that are associated with susceptibility to chronic Salmonella infection in cattle. This will be investigated by three specific objectives: In year 1, we will collect blood and fecal samples from dairy cattle in commercial herds with a history of natural infection with Salmonella. Assays to induce various cytokines of the host's cellular immune response will be performed using peripheral blood mononuclear cells (PBMC). Salmonella shedding will be detected by fecal cultures. Animals with chronic Salmonella infection as measured by persistent fecal shedding and cattle that recovered from infection will be identified. In year 2, the cytokines will be detected in all samples by ELISA. The cellular immune responses of both groups of cattle will be characterized and the results from all experiments will be evaluated. Immune parameters indicative for immunity (protective phenotype) or susceptibility to chronic Salmonella infection will be defined. In year 3, we will develop in vitro systems to modify the immune response in cells from cattle with chronic Salmonella infection towards the protective phenotype. Stimuli that trigger the immune response in vitro towards the protective phenotype are candidates for in vivo application and vaccine development.
NON-TECHNICAL SUMMARY: Salmonellosis is one of the most important foodborne diseases in humans and occurs worldwide. The increase in the development of multi-drug resistant Salmonella has resulted in increasing incidence and severity of the disease during the recent years. In humans, salmonellosis generally occurs after consumption of contaminated food of animal origin, such as meat, poultry, eggs and milk. This project focuses on dairy cattle in New York State as a potential source of Salmonella infection. We will investigate the natural immunity in cattle that results in protection from chronic Salmonella infection. We expect to define new mediators of immunity to Salmonella in cattle that are correlated with protection and prevent chronic Salmonella shedding. The outcomes can be used for the development of efficient vaccines to prevent salmonellosis in cattle and subsequently improve food safety and human health.
APPROACH: The immune response to Salmonella will be compared in two groups of adult cows from commercial dairy herds. Group 1 will include animals with chronic Salmonella infection. Group 2 will consist of cattle that have recovered from infection. Year 1: Herds with clinical outbreaks of salmonellosis will be identified. Blood and fecal samples will be obtained bi-monthly from laboratory-confirmed clinical cases. Fecal samples will be cultured for Salmonella using standard procedures. Cows that recover from infection as shown by at least 5 sequential culture-negative fecal samples will provide a comparison group. Cows that do not meet this citeria provide the group of chronic shedders. Samples will be collected for 4 months. Lymphocytes will be isolated from blood to monitor cellular immunity by re-stimulating the cells with Salmonella antigen in vitro. Supernatants collected from these cultures will be stored. Our goal is to enroll 50 cows in the study. Based on previous research, we expect 10-15 to shed Salmonella (chronic infected group). Year 2: Cytokines indicative for cellular immune responses will be detected in the supernatants using ELISA (IFN-g, IL-4, IL-10, TNF-a, IL-1b). The results will be evaluated to identify parameters of the immune response associated with recovery from Salmonella infection. Year 3: We will use the established immune parameters as read-outs to develop an in vitro model for influencing cellular immunity in cattle with chronic salmonellosis. PBMC from around 15-20 animals will be incubated with Salmonella antigen and recombinant cytokines (IFN-a, IL-2, IL-12) will be added as immune stimuli. Stimulated cells will be evaluated for shifting towards the protective phenotype by ELISA.