The role of antigen recognition in the γδ T cell response at the controlled stage of M. tuberculosis infection.

Abstract

{gamma}{delta} T cells contribute to host immune defense uniquely; but how they function in different stages (e.g., acute versus chronic) of a specific infection remains unclear. As the role of{gamma}{delta} T cells in early, active Mycobacterium tuberculosis (Mtb) infection is well documented, we focused on elucidating the{gamma}{delta} T cell response in persistent or controlled Mtb infection. Systems analysis of circulating{gamma}{delta} T cells from a South African adolescent cohort identified a distinct population of CD8+{gamma}{delta} T cells that expanded in this state. These cells had features indicative of persistent antigenic exposure but were robust cytolytic effectors and cytokine/chemokine producers. While these{gamma}{delta} T cells displayed an attenuated response to TCR-mediated stimulation, they expressed Natural Killer (NK) cell receptors and had robust CD16 (Fc{gamma}RIIIA)-mediated cytotoxic response, suggesting alternative ways for{gamma}{delta} T cells to control this stage of the infection. Despite this NK- like functionality, the CD8+{gamma}{delta} T cells consisted of highly expanded clones, which utilized TCRs with different V{gamma}/{delta} pairs. Theses TCRs could respond to an Mtb-lysate, but not to phosphoantigens, which are components of Mtb-lysate that activate{gamma}{delta} T cells in acute Mtb infection, indicating that the CD8+{gamma}{delta} T cells were induced in a stage-specific, antigen-driven manner. Indeed, trajectory analysis showed that these{gamma}{delta} T cells arose from naive cells that had traversed distinct differentiation paths in this infection stage. Importantly, increased levels of CD8+{gamma}{delta} T cells were also found in other chronic inflammatory conditions, including cardiovascular disease and cancer, suggesting that persistent antigenic exposure may lead to similar{gamma}{delta} T cell responses.