(A) Still images of the Movies EV3 (Control, upper panel) and EV4 (NEF, lower panel), obtained by intravital time lapse 2PM imaging of draining popliteal LNs 24hrs post immunization with HEL-OVA/CFA, following adoptive transfer of GFP BHEL cells (green) and mTomato CD4OT-II cells (red) expressing empty vector (Control; upper panel) or NEF WT (lower panel), respectively. High endothelial venules (HEVs) (white) were labeled by intravenous injection of Alexa660-labeled Meca-79 antibody and collagen (blue) is visualized by second harmonic generation (SHG). Yellow and orange arrows indicate stable and transient ISs, respectively. Numbering of ISs corresponds to that in the respective Supplemental movies. Scale bar 20µm. (B) Quantification of the duration of interactions as indicated by the arrows in A. Touching T and B cells were manually quantification using virtual reality (InViewR, Arivis). Each dot represents one T-B interaction pair. Red bar shows median. Data is derived from 5 to 6 movies, acquired from 4 mice in 2 independent experiments. Percentages on top indicate frequency of interactions that lasted 20min or longer. 