Movie 3

Antigen vesicles fuse with LysoTracker-positive vesicles hovering beneath the plasma membrane. A20 D1.3 cells were loaded with LysoTracker (middle panel) and activated with AF488-αIgM (left panel). Right panel shows merge image of antigen channel (magenta) and LysoTracker channel (cyan). Live-imaging was performed with SDCM (EVOLVE camera) on a single plane every 500 ms. An antigen vesicle fusing with LysoTracker after pinching from the plasma membrane is highlighted with a purple circle. Movie was recorded 80 s after activation.