The protoxin Cry1Ac of Bacillus thuringiensis improves the protection conferred by intranasal immunization with Brucella abortus RB51 in a mouse model

•Adjuvant protoxin Cry1Ac improves RB51 Brucella abortus vaccine.•Intranasal immunization confers protection against virulent challenge.•Co-administration of pCry1Ac and RB51 induces effective cellular immune responses.•Improved in vivo cytotoxic response and proliferation of T CD8+ cells.•Increased production of TNF-α, IFN-γ and specific IgG2a antibody titers.

Brucellosis is a zoonotic disease affecting many people and animals worldwide. Preventing this infection requires improving vaccination strategies. The protoxin Cry1Ac of Bacillus thuringiensis is an adjuvant that, in addition to increasing the immunogenicity of different antigens, has shown to be protective in different models of parasitic infections. The objective of the present study was to test whether the intranasal co-administration of pCry1Ac with the RB51 vaccine strain of Brucella abortus confers protection against an intranasal challenge with the virulent strain B. abortus 2308 in BALB/c mice. The results showed that co-administration of pCry1Ac and RB51, increased the immunoprotection conferred by the vaccine as evidenced by the following: (1) decrease of the splenic bacterial load when challenged intranasally with the virulent strain; (2) greater in vivo cytotoxic activity in response to the transference of previously infected cells; (3) further proliferation of cytotoxic TCD8+ cells in response to stimulation with heat-inactivated bacteria; (4) increased production of TNF-α and IFN-γ; and (5) significant IgG2a response. These results indicate that the use of the Cry1Ac protein as a mucosal adjuvant via the intranasal route can be a promising alternative for improving current RB51 vaccine against brucellosis.