Immune response of calves vaccinatedwith Brucella abortus S19 or RB51 and revaccinatedwith RB51

Abstract

Brucella abortus S19 and RB51 have been successfully used to control bovine brucellosis worldwide, however, at the present, most of our understanding of the protective immune response induced by vaccination comes from studies in mice. Therefore, the aim of this study was to characterize and compare the immune responses induced in the cattle prime immunized with B. abortus S19 or RB51 and RB51 revaccination. Calves aged 4 to 8 months were immunized with either vaccine S19 or RB51 on day 0, and revaccinated with RB51 on day 365 of the experiment. The characterization of the immune response was performed using serum and peripheral blood mononuclear cells. The blood samples were collected on days 0, 28, 210, 365, 393 and 575 post-immunization. Results showed that S19 and RB51 vaccination induced an immune response characterized by proliferation of CD4+ and CD8+ T-cells; IFN- and IL-17A production by CD4+ T-cells; cytotoxic CD8+ T-cells; IL-6 secretion; CD4+ and CD8+ memory cells; immunoglobulins of IgG1 class; and expression of the phenotypes of activation in T-cells. The differences in the immune response stimulated by S19 compared to RB51 were the higher persistency of IFN- and CD4+ memory cells, induction of CD21+ memory cells and higher secretion of IL-6. After RB51 revaccination, the immune response was chiefly characterized by increase in IFN- expression, proliferation of antigen-specific CD4+ and CD8+ T-cells, cytotoxic CD8+ T-cells and decrease in IL-6 production in both groups. However, a different polarization of the immune response, CD4- or CD8-dominant, was observed after the booster with RB51, for S19 and RB51 prime vaccinated animals, respectively. Our results indicate that after first vaccination both vaccine strains (S19 and RB51) induce a strong and complex immune response dominated by Th1 profile, though after RB51 revaccination the differences between immune profiles induced by prime vaccination become more accentuated.