Characterization of bovine γδ T cells phenotype following <i>Mycobacterium bovis</i> vaccination or virulent infection

Abstract Bovine tuberculosis caused by Mycobacterium bovis is a significant veterinary health problem. γδ T cells participate in the control of mycobacterial infections. Accumulating data suggest that mycobacterial infection regulates memory/effector phenotype and immune functions of mycobacterium-responsive γδ T cells. To date, the impact of both virulent M. bovis infection and Bacille Calmette-Guerin (BCG) vaccination on bovine γδ T cells memory/effector phenotype remains unknown. In this study, we addressed the functional and phenotypical differences in memory/activation marker, and chemokine receptor expression of M. bovis-specific γδ T cells following BCG vaccination or virulent M. bovis infection. Analysis of γδ T cells in blood, bronchoalveolar lavage fluid, and regional lymph nodes indicated that γδ T cells have phenotypic differences based on the expression of CD27 that suggest distinct functional properties. Here, we show that most peripheral γδ T cells display a CD27+ phenotype. Antigen recall responses showed that expression of CD27 correlates with the expansion of M. bovis-specific γδ T-cells. Thus, the CD27+ subset may comprise the adaptive γδ T cell compartment responding to virulent M. bovis infection and vaccination. Furthermore, we show that γδ T cells from neonatal calves are activated by aerosol BCG vaccination and adopt a lung-homing phenotype that is similar to that observed during virulent M. bovis infection, suggesting an important role for this T cell subset in the response to mucosal vaccination. The ability of γδ T cells to mount a robust local immune response supports the hypothesis that vaccine-elicited γδ T cell immunity might prove beneficial.