A model for lytic granule secretion at the IS. Secretion of cytotoxic granules at the IS involves 2 successive transport steps. First, a dynein-dependent transport step mediates the minus-end-mediated movement of cytotoxic granules to the MTOC.^8,9  Second, a plus-end kinesin-dependent transport step enables the polarized cytotoxic granules to reach the membrane and release their contents at the IS. In the latter step, granule-associated Rab27a recruits effector Slp3, which interacts with the kinesin-1 light chain (KLC1).