Yersinia enterocolitica as a vehicle for a naked DNA vaccine encoding Brucella abortus bacterioferritin or P39 antigen.

ABSTRACT

Brucella is a facultative intracellular parasite that causes brucellosis in animals and humans. The protective immune response against Brucella involves both humoral and cell-mediated immunity. In previous studies, we demonstrated that the T-dominant Brucella antigens bacterioferritin (BFR) and P39 administered either as CpG adjuvant recombinant proteins or as naked-DNA plasmids induced a specific Th1-biased immune response in mice. In order to improve the protection conferred by the BFR and P39 vaccines and to evaluate the additive role of antilipopolysaccharide (anti-LPS) antibodies, we used live attenuated Yersinia enterocolitica serotypes O3 and O9 as delivery vectors for naked-DNA plasmids encoding these BFR and P39 antigens. Following two intragastric immunizations in BALB/c mice, the Yersinia vectors harboring a DNA vaccine encoding BFR or P39 induced antigen-specific serum immunoglobulin and Th1-type responses (both lymphocyte proliferation and gamma interferon production) among splenocytes. Moreover, as expected, antibodies recognizing Brucella abortus 544 lipopolysaccharide were detected in O9-immunized mice but not in O3-treated animals. Animals immunized with O9 organisms carrying pCI or with O9 organisms alone were found to be significantly resistant to infection by B. abortus 544. Our data demonstrated that pCI plasmids encoding BFR or P39 and delivered with live attenuated strains of Yersinia O3 or O9 can trigger Th1-type responses. The fact than only O9 vectors induced a highly significant protective immunity against B. abortus 544 infection pointed out the crucial role of anti-LPS antibodies in protection. The best protection was conferred by a serotype O9 strain carrying pCIP39, confirming the importance of the P39 T-cell antigen in this mechanism.