title: Protective efficacy and immune responses by homologous prime-booster immunizations of a novel inactivated Salmonella Gallinarum vaccine candidate.
abstract: OBJECTIVE
  Salmonella enterica serovar Gallinarum (SG) ghost vaccine candidate was recently constructed. In this study, we evaluated various prime-boost vaccination strategies using the candidate strain to optimize immunity and protection efficacy against fowl typhoid.
  
  
  METHODS
  The chickens were divided into five groups designated as group A (non-immunized control), group B (orally primed and boosted), group C (primed orally and boosted intramuscularly), group D (primed and boosted intramuscularly), and group E (primed intramuscularly and boosted orally). The chickens were primed with the SG ghost at 7 days of age and were subsequently boosted at the fifth week of age. Post-immunization, the plasma IgG and intestinal secretory IgA (sIgA) levels, and the SG antigen-specific lymphocyte stimulation were monitored at weekly interval and the birds were subsequently challenged with a virulent SG strain at the third week post-second immunization.
  
  
  RESULTS
  Chickens in group D showed an optimized protection with significantly increased plasma IgG, sIgA, and lymphocyte stimulation response compared to all groups. The presence of CD4(+) and CD8(+) T cells and monocyte/macrophage (M/M) in the spleen, and splenic expression of cytokines such as interferon γ (IFN-γ) and interleukin 6 (IL-6) in the immunized chickens were investigated. The prime immunization induced significantly higher splenic M/M population and mRNA levels of IFN-γ whereas the booster showed increases of splenic CD4(+) and CD8(+) T-cell population and IL-6 cytokine in mRNA levels.
  
  
  CONCLUSIONS
  Our results indicate that the prime immunization with the SG ghost vaccine induced Th1 type immune response and the booster elicited both Th1- and Th2-related immune responses.
authors.affiliation: College of Veterinary Medicine, Chonbuk National University, Iksan, Korea.
authors.forename: Gayeon
authors.identifier: 0000-0003-4832-7937
authors.initials: G
authors.lastname: Won
authors.affiliation: College of Veterinary Medicine, Chonbuk National University, Iksan, Korea.
authors.forename: Atul A
authors.identifier: 0000-0002-5281-3252
authors.initials: AA
authors.lastname: Chaudhari
authors.affiliation: College of Veterinary Medicine, Chonbuk National University, Iksan, Korea.
authors.forename: John Hwa
authors.identifier: 0000-0002-2028-2207
authors.initials: JH
authors.lastname: Lee
keywords: Fowl typhoid; Ghost vaccine; Immunization scheme; Protection; Salmonella