Abstract
Cytotoxic immune cells mediate precise attacks against diseased cells to maintain organismal health. Their operational unit of killing and host defense is lytic granules (LGs), which are specialized lysosomal-related organelles. Precision in cytotoxicity is achieved by converging the many LGs to the microtubule-organizing center (MTOC) and polarizing these to the diseased cell for secretion. We identify unappreciated intimate relationships between the Golgi, MTOC, and LGs after cytotoxic cell activation, as well as the trans-Golgin protein GCC2 on the LG surface. GCC2 serves to tether LGs to the Golgi following convergence, and both GCC2 and the Golgi are required for the persistence of convergence. GCC2 allows LGs to utilize the Golgi as a docking station preventing LG dispersion and innocent bystander killing in complex three-dimensional environments. We also identify GCC2 variants causing human natural killer cell deficiency, further emphasizing the importance of LG convergence and Golgi linkage in precision targeting for human immunity.