Immunogenicity of a 16.7 kDa Mycobacterium paratuberculosis antigen

Mycobacterium paratuberculosis (MPT), the agent of paratuberculosis is a slow growing mycobacteria that causes important economic losses mainly due to lower weight gains and drastic decrease in milk production. Existing paratuberculosis vaccines are not completely protective and induce antibodies/delayed type hypersensitivity (DTH) reaction that cannot be differentiated from those of naturally infected animals. New potent acellular vaccines that allow discrimination between infected and vaccinated animals are needed to improve the control of this disease. We have identified, expressed and purified a hypothetical thiol peroxidase of MPT (MPT-TP) in mice. We also characterized the immunogenicity of this antigen in mice. The recombinant MPT-TP (rMPT-TP) antigen induced a high production of IFNgamma, IL-6, and NO and a low production of IL-10 by spleen cells of immunized mice. Addition of Ribi adjuvant to rMPT-TP resulted in lower IFNgamma secretion and higher NO production in spleen cells. A similar level of proliferation of spleen cells exposed to rMPT-TP was found in immunized groups (rMPT-TP and rMPT-TP emulsified in Ribi). DTH responses in mice footpads were observed only in mice immunized with rMPT-TP emulsified in Ribi. Addition of Ribi adjuvant clearly induced a significantly higher anti-rMPT-TP antibody production of all classes tested and decreased the IgG1/IgG2a ratio. MPT-TP demonstrated antigenic characteristics that make this antigen a potential component in the development of a future subunit vaccine against paratuberculosis.