Regulatory T-cell counter-regulation by innate immunity is a barrier to transplantation tolerance.

Innate immune signals foster adaptive immunity through activation of antigen-presenting cells. Recent in vitro evidence suggests that innate signaling may also contribute to immunity by countering the effects of regulatory T cells (T-regs), counter-regulation. We present in vivo evidence using a transgenic skin allograft model that the function of T-regs is lost in the setting of acute skin transplantation but remains intact when grafts were transplanted 1 month prior to allow surgery-induced inflammation to abate. Our findings identify T-reg counter-regulation as a naturally occurring process that accompanies transplantation and an important barrier to T-reg–mediated tolerance. Our finding further highlights the central role of regulatory cell deactivation in the initiation of the immune response.