Immune responses
Figure 2 shows immune responses, detected as secretion of IFNγ by peripheral blood cells stimulated with PPD-A or PPD-B. Blood samples were taken prior to and after vaccination at weeks 0, 4 and 8, as well as after intranodal BCG Tokyo challenge. No statistically significant difference was observed between the responses to PPD-A and responses to PPD-B in any of the animal groups at week 0. Similarly, there was no statistically significant difference in the response to PPD-B detected at weeks 4 and 8 compared to responses at week 0 in any of the animal groups regardless of their vaccination status. In non-vaccinated HF cattle, responses to PPD-A were greater than responses to PPD-B at week 8; in non-vaccinated Zebu cattle, responses to PPD-A were greater than responses to PPD-B at week 4; responses to PPD-A in HF vaccinated cattle were greater than the responses to PPD-B at weeks 4 and 8; and in vaccinated Zebu cattle responses to PPD-A were greater than responses to PPD-B at week 8. Interestingly, responses to PPDA or PPDB observed in vaccinated HF were indistinguishable from responses observed in unvaccinated HF calves.
Eight weeks after subcutaneous vaccination with BCG all cattle were inoculated intranodally with c 107 cfu of BCG Tokyo in the challenge phase of the experiment. Responses to intranodal inoculation were also evaluated by measuring the production of IFNγ responses by peripheral blood cells stimulated with PPD-A and PPD-B at 1 and 2 weeks post-intranodal challenge (weeks 9 and 10 after the initial BCG vaccination, respectively) (figure 2). The data indicated that, following challenge with BCG, the responses to PPD-A or PPD-B detected at weeks 9 and 10 in vaccinated or not vaccinated HF cattle were not different from the responses detected at week 8, prior to challenge; this was similar to what was observed in vaccinated Zebu cattle, i.e. no difference in responses at weeks 9 and 10 compared to responses observed in week 8. In contrast, in non-vaccinated Zebu cattle, intranodal challenge induced a statistically significant increase in the responses to PPD-A at week 9 (ρ < 0.001) but not at week 10; intranodal inoculation in the same group of animals induced a statistically significant increase in responses to PPD-B at weeks 9 (ρ < 0.001) and 10 (ρ < 0.05).