miR-146a controls the resolution of T cell responses in mice . T cell responses in mammals must be tightly regulated to both provide effective immune protection and avoid inflammation-induced pathology. NF-kappaB activation is a key signaling event induced by T cell receptor (TCR) stimulation. Dysregulation of NF-kappaB is associated with T cell-mediated inflammatory diseases and malignancies, highlighting the importance of negative feedback control of TCR-induced NF-kappaB activity. In this study we show that in mice, T cells lacking miR-146a are hyperactive in both acute antigenic responses and chronic inflammatory autoimmune responses. TCR-driven NF-kappaB activation up-regulates the expression of miR-146a, which in turn down-regulates NF-kappaB activity, at least partly through repressing the NF-kappaB signaling transducers TRAF6 and IRAK1 . Thus, our results identify miR-146a as an important new member of the negative feedback loop that controls TCR signaling to NF-kappaB . Our findings also add microRNA to the list of regulators that control the resolution of T cell responses.