Vaccination of calves with Mycobacteria bovis Bacilli Calmete Guerin (BCG) induced rapid increase in the proportion of peripheral blood gammadelta T cells.

Changes in the proportion of peripheral blood T cell subsets after subcutaneous inoculation of cattle with Mycobacterium bovis Bacille Calmette-Guerin (BCG) were studied. Calves were injected with approximately 8 x 10(6) BCG bacillus and blood samples collected at weekly intervals for flow-cytometric analyses to determine the proportion of CD4+, CD8+ and gammadelta T cells. In addition, whole blood samples were stimulated in vitro with M. bovis purified protein derivative (PPD) and the secreted IFN-gamma quantified by ELISA. Results showed cellular and cytokine changes which could be categorized into three phases. The first phase occurred within the first 2 weeks after vaccination involving an increase in proportion of WC1+ gammadelta T cells and a concomitant increase in the secretion of IFN-gamma. These two responses peaked at 2 weeks and waned thereafter. The second phase involved an increase in the CD4/CD8 ratio as a result of an increase in the proportion of CD4+ T cells between 4 and 6 weeks. The third phase involved a decrease in the CD4/CD8 ratio due to an increase in the proportion of CD8+ T cells between 8 and 10 weeks. Surprisingly, the IFN-gamma response was associated with changes in the gammadelta rather than the CD4+ or CD8+ T cells, suggesting that this cytokine was secreted by gammadelta-T cells. These results are consistent with the reported ability of gammadelta T cells to act rapidly and bridging the innate and classically adaptive immune responses.