Noninvasive intravital visualization of T_reg–T_eff cell contact in target tissue. (A) Snapshots from representative time-lapse recordings demonstrating stable, long-lasting interaction between CD4⁺ T_reg–T_eff interactions within the islet tissue. The majority of interactions lasted for the entire time of the recordings (≥30 min; see Video 4). Absolute (B) and relative (C) interaction time between the CD4⁺BDC2.5 T_eff and T_reg cells (n = 50 cell pairs; mean ± SEM). Relative interaction time is calculated by dividing absolute interaction time with total imaging session length. Of note, many of the interactions were already established at the beginning of imaging; hence, actual interaction times are likely longer than those measured during the in vivo imaging timeframe which is limited by the animals’ tolerance of general anesthesia. Data points represent one T_reg–T_eff pair and lines represent the mean ± SEM. The interaction index (D) and velocity (E) of both T_eff and T_reg cells in a mode of contact interaction or not (n = 55–100 cells; mean ± SEM). Data represent three experiments with 6 mice. ***, P < 0.001. Bar, 30 µm.