F18+Escherichia coli flagellin expression in Salmonella has immunoadjuvant effects in a ghost vaccine candidate containing E. coli Stx2eB, FedF and FedA against porcine edema disease

Flagellin, a major structural component of bacteria flagella, is responsible for facilitating motility and invading host cells. The binding capacity of flagellin to toll-like receptor 5 (TLR5) and its trigger action for innate immunity make it an attractive vaccine adjuvant. In this work, we explored the efficacy of F18+STEC flagellin as an adjuvant in a ghost vaccine candidate against porcine edema disease (ED). TLR5-stimulating activity and IL-8 cytokine expression produced via downstream signaling following ligand exposure was detected in HEK-Blue™-hTLR5 cells stimulated with flagellin expressed in the Salmonella Typhimurium (ST) ghost, JOL1485. Mice immunized with JOL1485 mixed with the vaccine candidate showed significantly increased secretory IgA specific to flagellin during the study period. JOL1485 efficiently induced maturation of naïve dendritic cells, resulting in production of immunomodulatory cytokines associated with Th1 and Th2 immunity. Particularly, marked increases in IL-6 inducing B-cell differentiation and IL-12 associated with Th1 immunity were observed in CD4 + T-cells stimulated with JOL1485 primed DCs. Furthermore, all mice immunized with JOL1485 mixed with the vaccine candidate showed higher protection efficacy against challenge and significantly enhanced clearance of the challenge strain, compared to mice immunized with only the vaccine candidate. Collectively, these results indicated that flagellin expression in JOL1485 may have immunostimulatory properties that serve as a potent adjuvant for the vaccines against ED.