Abstract
Natural killer (NK) cells contain specialized lysosome-related organelles termed lytic granules allowing them to mediate cytotoxicity against tumorigenic or virally infected target cells. NK cells polarize their lytic granules toward a target cell via the microtubule-organizing center (MTOC). Prior to that, however, lytic granules converge to the MTOC along microtubules utilizing minus-end-directed microtubule motors. Herein we describe how to visualize and quantify lytic granule convergence using confocal microscopy to gain quantitative insight into NK cell cytotoxicity and its regulation.