N-terminus of flagellin enhances vaccine efficacy against Actinobacillus pleuropneumoniae

BACKGROUND: Flagellin elicits potent immune response and may serve as a vaccine adjuvant. We previously reported that the N-terminus of flagellin (residues 1–99, nFliC) is sufficient for vaccine efficacy enhancement against Pasteurella multocida challenge in chickens. In this study, we futher tested the adjuvancy of nFliC in a subunit vaccine against the pig pathogen Actinobacillus pleuropneumoniae in a mice model. For vaccine formulation, the antigen ApxIIPF (the pore-forming region of the exotoxin ApxII) was combined with nFliC, either through genetic fusion or simple admixture. RESULTS: Immune analysis showed that nFliC, introduced through genetic fusion or admixture, enhanced both humoral (antibody levels) and cellular (T cell response and cytokine production) immunity. In a challenge test, nFliC increased vaccine protective efficacy to 60–80%, vs. 20% for the antigen-only group. Further analysis showed that, even without a supplemental adjuvant such as mineral salt or oil emulsion, genetically linked nFliC still provided significant immune enhancement. CONCLUSIONS: We conclude that nFliC is a versatile and potent adjuvant for vaccine formulation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12917-022-03380-8.