Date of Graduation

8-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Erf, Gisela F.

Committee Member

Alrubaye, Adnan

Second Committee Member

Jesudhasan, Palmy

Third Committee Member

Sun, Xiaolun

Keywords

Antibody response; Egg-type pullets; Local cellular immune response; Salmonella vaccines; Systemic immune response

Abstract

Salmonella infection in chickens is a significant and complex challenge to manage, affecting poultry health and food safety. Vaccination against Salmonella is a promising preventative approach to control flock infection and decrease the loads of this pathogen. Vaccination strategies against Salmonella often comprise the application of live attenuated and killed (inactivated) vaccines, including inactivated autogenous vaccines. Live attenuated Salmonella vaccines stimulate both cellular and humoral immunity but can potentially return to a virulent state; meanwhile, inactivated Salmonella vaccines trigger more of a humoral response and are safer since they are entirely rendered inactive. However, there is a lack of information on the cellular immune mechanisms occurring at the site of administration of inactivated Salmonella vaccines, limiting our understanding of how these vaccines can trigger chickens' immune defenses and how they could be improved. The dual-window approach, which comprises the growing feather (GF)-pulp test system and concurrent blood sampling, has been established as a minimally invasive comprehensive tool for monitoring in vivo local tissue/cellular and systemic immune responses to i.d. GF-pulp administration of test materials. In this dissertation project, the dual-window approach was used to monitor and assess the local- and systemic-cellular and humoral immune responses following different inactivated Salmonella vaccines and their components to gain insights into the impact of formulation, method of inactivation, route of administration, and antigen re-exposure on innate and adaptive immune responses in egg-type pullets. Administration of inactivated Salmonella vaccines or their components into GF-pulp stimulated tissue/cellular inflammatory responses, distinguished by the recruitment of different leukocytes from the blood into the GF-pulp, influencing circulating blood leukocyte profiles and leading to robust T-dependent Salmonella-specific antibody production in the plasma characterized by isotype switching from IgM to IgG and IgA. This investigation provides comprehensive knowledge about the temporal, quantitative, and qualitative local- and systemic-cellular and humoral immune responses to different inactivated Salmonella vaccines and their components in chickens. Overall, these findings not only provide practical insights for the development of inactivated Salmonella vaccines that can effectively stimulate protective levels of immunity against Salmonella in chickens but also serve as a basis for future investigations on the understanding of local and systemic immune responses to other types of immune modulators that can enhance poultry health.

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