γδ T Cell Homeostasis Is Controlled by IL-7 and IL-15 Together with Subset-Specific Factors

Among T cell subsets, gamma delta T cells uniquely display an Ag receptor-based tissue distribution, but what defines their preferential homing and homeostasis is unknown. To address this question, we studied the resources that control gamma delta T cell homeostasis in secondary lymphoid organs. We found that gamma delta and alpha beta T cells are controlled by partially overlapping resources, because acute homeostatic proliferation of gamma delta T cells was inhibited by an intact alpha beta T cell compartment, and both populations were dependent on IL-7 and IL-15. Significantly, to undergo acute homeostatic proliferation, gamma delta T cells also required their own depletion. Thus, gamma delta T cell homeostasis is maintained by trophic cytokines commonly used by other types of lymphoid cells, as well as by additional, as yet unidentified, gamma delta-specific factors.