Immune response to inactivated bacterial vector carrying the recombinant K39 antigen of Leishmania infantum in mice

Abstract

Objective: To evaluate the immunological response elicited by an inactivated bacterial vector carrying the K39 antigen of Leishmania infantum, and a purified antigen. Methods: Mice were subjected to the following treatments: (1) Purified recombinant K39 (rK39) protein at a 20 μg dose with complete Freund’s adjuvant; (2) Inactivated Escherichia coli (BL21 DE3) carrying the K39 protein at an equivalent total protein content of 200 μg; (3) Inactivated bacteria lacking the K39 protein; (4) Non-immunized control animals. Serological monitoring was performed. All groups were challenged by intraperitoneal injection of 10⁷ Leishmania infantum promastigotes. After euthanasia, the liver and spleen were collected to analyze the levels of TNF, IFN-γ, IL-12, IL-4, and IL-10. Results: Mice immunized with purified rK39 or the inactivated bacterial vector carrying the K39 antigen of Leishmania infantum showed a long-lasting immune response with high levels of polyclonal antibodies specifically recognizing the recombinant proteins. The IgG1 subclass was the predominant immunoglobulin; however, the induction of IgG2a and the profile of cytokines produced were indicative of the induction of a mixed-type response. Conclusions: The inactivated bacterial vector carrying the K39 antigen, as well as the purified antigen can induce a long-lasting immune response in immunized mice, predominantly favouring a Th2 profile response.

Keywords

Visceral leishmaniasis / K39 / Inactivated bacterial vector / Vaccine / Immune response / Th1 / Th2 / Leishmania infantum

Conflict of interest statement

The authors declare that there is no conflict of interest.

Funding

This work was supported by grants from the Brazilian Agencies: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES-Financial code 001), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico (FUNCAP).

Data availability statement

The data supporting the findings of this study are available from the corresponding authors upon request.

Authors’ contributions

LSA designed the work, conducted the experimental studies, performed data acquisition and analysis, and prepared, edited, and reviewed the manuscript. BBS conducted the experimental studies, performed data acquisition and analysis, and prepared, edited, and reviewed the manuscript. ENFNS, ASB, and SSF conducted the experimental studies and reviewed the manuscript. ARM performed statistical analysis and reviewed the manuscript. EOPTF reviewed the manuscript. Both MFvT and MIFG designed the work, performed data analysis, and prepared, edited, and reviewed the manuscript.

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