Expression of Babesia bovis rhoptry-associated protein 1 (RAP1) in Brucella abortus S19

Brucella abortus strain 19 (live vaccine) induces a strong humoral and cellular immune response and therefore, it is an attractive vector for the delivery of heterologous antigens. The objective of the present study was to express the rhoptry-associated protein (RAP1) of Babesia bovis in B. abortus S19, as a model for heterologous expression of immunostimulatory antigens from veterinary pathogens. A plasmid for the expression of recombinant proteins fused to the aminoterminal of the outer membrane lipoprotein OMP19 was created, pursuing the objective of increasing the immunogenicity of the recombinant antigen being expressed by its association to a lipid moiety. Recombinant strains of B. abortus S19 expressing RAP1 as a fusion protein either with the first aminoacids of β-galactosidase (S19pBB-RAP1) or B. abortus OMP19 (S19pBB19-RAP1) were generated. Plasmid stability and the immunogenicity of the heterologous proteins were analyzed. Mice immunized with S19pBB-RAP1 or S19pBB19-RAP1 developed specific humoral immune response to RAP1, IgG2a being the predominant antibody isotype. Furthermore, a specific cellular immune response to recombinant RAP1 was elicited in vitro by lymphocytes from mice immunized with both strains. Therefore, we concluded that B. abortus S19 expressing RAP1 is immunostimulatory and may provide the basis for combined heterologous vaccines for babesiosis and brucellosis.