(C) HEL-OVA pulsed- BHEL cells (blue) and CD4OT-II cells (green) were placed on PLL-coated cover glasses and subjected to live-cell time-lapse imaging. Shown are representative still images. BHEL cells were loaded with SiRAct to visualize actin polymerization in B cells (F-actin displayed in red). Filled and empty arrowheads indicate presence or absence of F-actin accumulation at the IS, respectively. Scale bars, 5µm. 