The time-lapse movie shows the brighter cell approaching two B cells and making them two ISs by recruiting TCR-CD3z (CFP fluorescence pseudocolored green) and CD4 (YFP fluorescence in red). LK35 cells were labeled with Cy5 and are shown in blue. Initially, the interaction is very dynamic with extensive membrane ruffling, contractions, spreading, and changes in cell shape. These movements subside after three minutes. Note another, dimmer A18.ZC.4Y cell approaching from below the frame. This cell makes contact with one APC and clusters CD4 andCD3z but then continues crawling and rapidly disassembles the IS. When it crawls away, it remains attached to the APC with a thin tether.