Class II MHC–independent suppressive adhesion of dendritic cells by regulatory T cells in vivo

Regulatory T (T reg) cells are essential for peripheral homeostasis and known to target and suppress dendritic cells (DCs). One important mechanism is through prolonged interaction between antigen-specific T reg cells and DCs that down-regulates the co-stimulatory capacity of DCs. However, the dynamics and TCR specificities of such T reg cell–DC interaction and its relevance to the suppressive outcomes for individual DCs have not been clarified. To gain insights into the underlying cellular events in vivo, we analyzed individual T reg cell–DC interaction events in lymph nodes by intravital microscopy. Our results show that, upon exposure to interleukin-2, T reg cells formed prolonged adhesive contact with DCs, independent of antigen or MHC recognition, which significantly suppressed the contemporaneous interaction of the same DCs with antigen-specific conventional T cells and impaired T cell priming. Therefore, T reg cells may function in part as feedback regulators in inflammatory milieu, by suppressing local DCs and interrupting immune activation in a contact-dependent and class II MHC-independent manner.