γδ TCRs Function as Innate-like Receptors in the Bovine γδ T Cell Response against Leptospira .

serovar Hardjo are bacterial pathogens of cattle that also cause zoonotic disease in humans. Vaccine-mediated protection against serovar Hardjo in cattle is associated with a workshop cluster 1 (WC1) γδ T cell response that can be recalled in vitro from PBMC by antigenic stimulation. This provides a model system in which to examine protective vaccine-induced γδ T cell responses in a γδ T cell high species. Only a small proportion (5-10%) of WC1 γδ T cells from immunized cattle are responders, implying that Ag specificity is determined by clonally distributed receptors. Both WC1 and TCR are known to be required for -specific responses by bovine WC1 γδ T cells. Through variegated expression patterns and V(D)J recombination, respectively, they have the capacity to confer Ag specificity. In this study, we develop and use a high-throughput TCR-sequencing approach to study the TCRγ and TCRδ repertoires of naive ex vivo PBMC, -responding, and nonresponding WC1 γδ T cells to examine the potential role of γδ TCR in determining Ag specificity. Our results provide novel insights into the PBMC γδ TCR repertoires in cattle, demonstrating the TCRγ repertoire to be clonally stratified and essentially public, whereas the TCRδ repertoire shows much higher levels of clonal diversity and is essentially private. TCR repertoire analysis of -responding WC1 γδ T cells identifies no signature of TCR-mediated selection, suggesting that TCR functions largely as an innate-like receptor and does not act as a primary determinant of Ag specificity in the response to this pathogen.