Endogenous T_regsshow stable interactions with host DCs and interfere with the interaction between donor T cells and DCs in the LNs. (A-C) Intravital imaging of donor T cells (labeled with CMTPX) and host DCs in the popliteal LNs of irradiated CD11c-DTR-EGFP mice in the presence (T_con:T_reg ratio of 3:2) or absence of unlabeled T_regs. In the absence of T_regs, unlabeled T cells were injected to provide an identical number of donor cells. (A) The mean velocity of donor T cells in the presence or absence of eT_regs from 4 to 24 hours (hr) posttransplant. (B) The time course of the displacement ratio of donor T-cell movement in the presence or absence of eT_regs. (C) Contact time between donor T cells and host DCs with or without eT_regs at different time points posttransplant. (D-G) Intravital imaging of donor eT_regs (labeled with CMTPX) and host DCs in the presence of unlabeled T_cons. (D) Still image from movies of eT_reg (red) with DCs (green). (E) Comparison of mean velocity between eT_regs and T_cons cells at various time points after transplant. (F) Contact time between eT_regs and host DCs, compared with contact time between donor T cells and DCs. (G) Comparison of mean velocity between eT_regs and T_cons when they were injected into the same recipient. The bars in all graphs represent median values. Asterisks indicate statistically significant differences between time points (*P < .05) or P value is shown. Data are representative of 2 separate experiments with 1 mouse imaged per condition per experiment.