Salmonella enterica serovar Enteritidis (S. Enteritidis, SE)
infection in broilers causes a huge economic loss and public health risk. We previously demonstrated that orally delivered
chitosan based (CS) Salmonella subunit nanoparticle (NP)
vaccine containing immunogenic outer
membrane proteins (OMP) and
flagellin (FLA) of SE [CS-NP(OMP+FLA)] induces immune response in broilers. The objective of this study was to evaluate the dose- and age-dependent response and efficacy of CS-NP(OMP+FLA)
vaccine in broilers. Three-day old birds were vaccinated and boosted once or twice. Additional groups were vaccinated at three weeks with no booster or boosted once a week later. Each dose of CS-NP
vaccine had either 10 or 50 μg of OMP+FLA
antigens. Our data revealed that two doses of
vaccine were required to induce substantial immune response. Birds received 2 doses of CS-NP(OMP+FLA)
vaccine at 3 days and 3 weeks of age with 10 μg
antigens, and birds inoculated twice at 3 and 4 weeks of age with 50 μg
antigens had lowest challenged bacterial load in the cecal contents with over 0.5 log10 reduction. In CS-NP(OMP+FLA) vaccinated birds,
antigen-specific splenocyte proliferation, mucosal and systemic antibody response and the frequency of IFNγ-producing T cells were increased compared to control groups. At the molecular level, in the cecal tonsils of CS-NP(OMP+FLA) immunized birds,
mRNA levels of
toll-like receptor (TLR) 2 and TLR 4, and
cytokines IL-4 and
IL-10 were upregulated. The CS-NP(OMP+FLA)
vaccine given orally has the potential to induce a protective immune response against SE
infection in broilers.