(C) Still images of the Movies EV5 (Control, upper panel) and EV6 (NEF, lower panel), obtained by intravital time lapse 2PM imaging of draining popliteal LNs 8d 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). Follicular dendritic cells (FDCs) (white) were labeled by subcutaneous injection of Alexa647-labeled anti-CD21/CD35 antibody and collagen (blue) is visualized by 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. (D) Quantification of the duration of interactions as indicated by the arrows in C. 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. Shown is one representative dataset out of two, derived from 5 to 8 movies, acquired from 4 mice. Percentages on top indicate frequency of interactions that lasted 20min or longer. 