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

Abstract

Summaryγδ 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 γδ T cells in early, active Mycobacterium tuberculosis (Mtb) infection is well documented, we focused on elucidating the γδ T cell response in persistent or controlled Mtb infection. Systems analysis of circulating γδ T cells from a South African adolescent cohort identified a distinct population of CD8+ γδ 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 γδ T cells displayed an attenuated response to TCR-mediated stimulation, they expressed Natural Killer (NK) cell receptors and had robust CD16 (FcγRIIIA)-mediated cytotoxic response, suggesting alternative ways for γδ T cells to control this stage of the infection. Despite this NK- like functionality, the CD8+ γδ T cells consisted of highly expanded clones, which utilized TCRs with different Vγ/δ pairs. Theses TCRs could respond to an Mtb-lysate, but not to phosphoantigens, which are components of Mtb-lysate that activate γδ T cells in acute Mtb infection, indicating that the CD8+ γδ T cells were induced in a stage-specific, antigen-driven manner. Indeed, trajectory analysis showed that these γδ T cells arose from naive cells that had traversed distinct differentiation paths in this infection stage. Importantly, increased levels of CD8+ γδ T cells were also found in other chronic inflammatory conditions, including cardiovascular disease and cancer, suggesting that persistent antigenic exposure may lead to similar γδ T cell responses.