This study aimed to investigate the adjuvant effect of recombinant attenuatedSalmonellaexpressing cholera toxin B subunit (CTB) andEscherichia coliheat-labile enterotoxin B subunit (LTB) for the P-fimbriae subunit-based vaccine of avian pathogenicE. coli(APEC) in a murine model. The PapA-specific sIgA and IgG responses were significantly enhanced after immunisation with theSalmonella-PapA vaccine in the presence of CTB or LTB. The group immunised with theSalmonella-LTB strain promoted Th1-type immunity, whereas that immunised with theSalmonella-CTB strain produced Th2-type immunity. We concluded that bothSalmonella-CTB and -LTB strains can enhance the immune response to PapA, and that the LTB strain may be a more effective adjuvant for APEC vaccination, which requires higher Th1-type immunity for protection. Thus, our findings provide evidence that immunisation with an adjuvant, LTB, is one of the strategies of developing effective vaccines against P-fimbriated APEC.
The B subunits of cholera and Escherichia coli heat-labile toxins enhance the immune responses in mice orally immunised with a recombinant live P-fimbrial vaccine for avian pathogenic E. coli