Conserved domains of flagellin as adjuvants for an inactivated vaccine against porcine epidemic diarrhea virus

Flagellin activates immune response through Toll-like Receptor 5 (TLR5) and can serve as a vaccine adjuvant. In this study, we evaluated the adjuvancy of the conserved domains of flagellins from three different bacteria: Salmonella typhimurium, Bacillus subtilis, and Bacillus cereus. The conserved domains were recombinantly expressed, and all three recombinant proteins demonstrated robust TLR5 activation in vitro. The recombinant proteins were formulated with inactivated porcine epidemic diarrhea virus (PEDV) as vaccines and mice were vaccinated for immune evaluation. Results showed that all three recombinant proteins enhanced proinflammatory response (IL-6 and TNF-α), cellular immunity, and PEDV-specific antibody response, when compared to the PEDV-alone group. In a virus neutralization test, all three recombinant proteins significantly enhanced the neutralization titer elicited by the PEDV vaccine. We conclude that despite differences in their sequences, conserved domains of flagellins from the three bacteria can activate TLR5 and may serve as vaccine adjuvants.