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).