Engineered Salmonella Enteritidis vector targeting innate immune molecules provides protection against Salmonella Enteritidis and Salmonella Typhimurium.

Targeting the innate immune response is a critical factor in vaccine success. There are numerous serotypes of Salmonella, and cross-reactivity among different serotypes or even strains within the same serotype is limited. This makes it difficult for vaccines to provide broad protection, posing a challenge to effective prevention and control. In this study, a Salmonella Enteritidis (S. Enteritidis) candidate vaccine strain, rSC0163, with high immunogenicity, was constructed by introducing the Salmonella mRNA interferase-regulating vector (SIRV) system. The rSC0163 strain, enhanced by the SIRV system, targets the host's innate immune cyclic GMP-AMP synthase (cGAS) molecule, triggering downstream immune pathways and significantly increasing levels of antibodies (IgA and IgY) and cytokines (IFN-γ and IL-4) in the peripheral blood of immunized chickens. Compared with the control strain rSC0162, the antiserum from chickens immunized with rSC0163 showed significantly enhanced opsonophagocytic activity. The highest opsonophagocytic assay (OPA) titers against the S. Enteritidis C50041 strain, S. Enteritidis CVCC3949 strain, and Salmonella Typhimurium (S. Typhimurium) UK-1 strain reached 1:256, 1:128, and 1:64, respectively. Furthermore, rSC0163 provided 100 % and 83 % protection against lethal doses of the C50041 and CVCC3949 strains, respectively, and 66 % protection against the heterologous S. Typhimurium UK-1 strain. These protection rates were significantly higher than those induced by rSC0162. In conclusion, integrating the SIRV system into the attenuated S. Enteritidis vector enhances both innate and adaptive immune responses, offering a basis for developing cross-serotype protective vaccines and Salmonella-based delivery platforms targeting other pathogens.