Abstract
The purpose of this study was to compare the immunological response induced by bovine brucellosis vaccination (S19 and RB51) in calves vaccinated in different ages between 3 and 8 months, to determine the ideal age for vaccination of calves. One hundred and five female calves aged 3 to 8 months were randomly divided in nine groups (n=12), in a 3x3 (3 vaccination regimens x 3 ages) experimental design, as follows: three groups were vaccinated with S19 at 3-4 (G1), 5-6 (G2) or 7-8 (G3) months of age, three groups were vaccinated with RB51 at 3-4 (G4), 5-6 (G5) or 7-8 (G6) months of age and three groups were inoculated with saline (controls) at 3-4 (G7), 5-6 (G8) or 7-8 (G9) months of age. Vaccination of all groups occurred at day 0 and assays to evaluate the induced immune response were performed at days 0, 28 and 56 after vaccination, from peripheral blood from all heifers at each time point. Peripheral blood mononuclear cells (PBMC) were isolated and cultured in the presence of γ irradiated Brucella abortus 2308 antigen to quantify CD4+, CD8+, CD4+CD45RO+ and CD8+CD45RO+ T lymphocytes. Culture supernatants were also tested for IFN-γ by ELISA. For each response variable, we fitted a mixed model with a fixed effect for the interaction age (3-4, 5-6 and 7-8) x treatment (S19, RB51 and control) × time (0, 28 and 56), using the packages lme4 and emmeans in the software R. The model for IFN-Ɣ production by the PBMC following vaccination exhibited a significant interaction only treatment and time, showing no effect of the age on vaccination. There was a significant higher expression of IFN-Ɣ after vaccination with S19 or RB51 at 28- and 56-days post-vaccination in comparison with control animals regardless the age of the calves, however, non-significant difference was observed between S19 and RB51 at any time or age. In conclusion, our results showed no effect of the age (3 to 8 months) on the immune response induced by vaccination of heifers with either S19 and RB51, as well as that both vaccines elicited a strong IFN-Ɣ response after vaccination.
