Innate-like T cells straddle innate and adaptive immunity by altering antigen-receptor responsiveness

T cell hyporesponsiveness is generally framed in terms of tolerance induction. Hayday and colleagues show that attenuating TCR responsiveness is also critical for the development of innate-like T cells that mediate the surveillance of dysregulated tissues. The subclassification of immunology into innate and adaptive immunity is challenged by innate-like T lymphocytes that use innate receptors to respond rapidly to stress despite expressing T cell antigen receptors (TCRs), a hallmark of adaptive immunity. In studies that explain how such cells can straddle innate and adaptive immunity, we found that signaling via antigen receptors, whose conventional role is to facilitate clonal T cell activation, was critical for the development of innate-like T cells but then was rapidly attenuated, which accommodated the cells' innate responsiveness. These findings permitted the identification of a previously unknown innate-like T cell subset and indicate that T cell hyporesponsiveness, a state traditionally linked to tolerance, may be fundamental to T cells entering the innate compartment and thereby providing lymphoid stress surveillance.