Maturation of resistance to salmonellosis in newly hatched chicks: inhibition by cyclosporine.

The development of resistance to salmonellosis and the basis of resistance in newly hatched chickens were investigated. Newly hatched chickens are inherently susceptible to salmonellosis but develop resistance rapidly to Salmonella infection during the first 5 days of life. Newly hatched chickens were treated with cyclosporine, the thymic (T)-cell-specific, immunosuppressive agent (T-cell). The resultant changes in T-cell responsiveness to mitogens, in vivo delayed-type hypersensitivity, and resistance to salmonellosis were measured. The results demonstrated that cyclosporine reduced in vitro T-cell responses to T-cell-specific mitogens, suppressed in vivo delayed-type hypersensitivity (tuberculin skin-test reactions), and impaired the development of native resistance to salmonellosis. These results indicate that development of resistance to salmonellosis in newly hatched chicks depends on a fully functional capacity for cell-mediated immunity. Therefore, the development of effective vaccines for reducing the contamination of live birds with Salmonella probably should include strategies for enhancing the early development of cellular immunity.