Homeodomain only protein is required for the function of induced regulatory T cells in dendritic cell-mediated peripheral T cell unresponsiveness

Induced T regulatory (iT(reg)) cells can be generated by peripheral dendritic cells (DCs) that mediate T cell-unresponsiveness to re-challenge with antigen. The molecular factors required for the function of such iT(reg) cells remain unknown. We report a critical role for the transcription co-factor Homeodomain only protein (Hop, also know as Hopx) in iT(regs) cells to mediate T cell unresponsiveness in vivo. Hopx-sufficient iT(reg) cells down-regulate the expression of the AP-1 complex and suppress other T cells. In the absence of Hopx, iT(reg) cells express high levels of the AP-1 complex, proliferate and fail to mediate T cell-unresponsiveness to re-challenge with antigen. Thus, Hopx is required for the function of T(reg) cells induced by DCs and the promotion of DC-mediated T cell unresponsiveness in vivo.