Local Inflammatory and Systemic Antibody Responses Initiated by a First Intradermal Administration of Autogenous Salmonella-Killed Vaccines and Their Components in Pullets

Vaccination strategies are used to manage <i>Salmonella</i> in chickens. <i>Salmonella</i>-killed vaccines are considered safer since they are inactivated. However, little is known regarding the cellular immune activities at the site of vaccine administration of <i>Salmonella</i>-killed vaccines. The growing feather (GF) cutaneous test has been shown to be an effective bioassay to monitor local tissue/cellular responses. We assessed local and systemic antibody responses initiated by intradermal injection of <i>Salmonella</i>-killed vaccines into GF-pulps of 14-15-week-old pullets. Treatments consisted of two autogenous <i>Salmonella</i>-killed vaccines (SV1 and SV2), <i>S.</i> Enteritidis (SE) lipopolysaccharide (SE-LPS), and the water-oil-water (WOW) emulsion vehicle. GF-pulps were collected before (0 h) and at 6, 24, 48, and 72 h post-GF-pulp injection for leukocyte population analysis, while heparinized blood samples were collected before (0 d) and at 3, 5, 7, 10, 14, 21, and 28 d after GF-pulp injections to assess plasma levels (a.u.) of SE-specific IgM, avian IgY (IgG), and IgA antibodies using an ELISA. Injection of GF-pulps with SV1, SV2, or SE-LPS, all in a WOW vehicle, initiated inflammatory responses characterized by the recruitment of heterophils, monocytes/macrophages, and a few lymphocytes. The WOW vehicle emulsion alone recruited more lymphocytes than vaccines or SE-LPS. The SV1 and SV2 vaccines stimulated <i>Salmonella</i>-specific IgM and IgA early, while IgG levels were greatly elevated later during the primary response. Overall, SV1 and SV2 stimulated a heterophil and macrophage-dominated local inflammatory- and SE-specific humoral response with an isotype switch from IgM to IgG, characteristic of a T-dependent primary antibody response. This study provides comprehensive information on innate and adaptive immune responses to autogenous <i>Salmonella</i>-killed vaccines and their components that will find application in the management of <i>Salmonella</i> in poultry.