Movie 4

Surface MHCII is internalised together with the antigen after activation. A20 D1.3 cells were labelled on ice with AF488-anti-MHCII (left panel) and RRx-αIgM (middle panel). Cells were shifted at 37 °C to start activation and recorded after 40 s. Right panel shows merge image of antigen channel (magenta) and MHCII channel (cyan). Live-imaging was performed with SDCM (sCMOS Orca Flash4 v2 camera) on a single plane every 4 s. Vesicles positive for MHCII and antigen were tracked with circles (shown in different colours) in the antigen channel.