The responses of cloned human NK cells (ERNK57) to seven CC chemokines (monocyte chemotactic protein-1 (MCP-1), MCP-2, MCP-3, RANTES (regulated on activation, normal T cell expressed and secreted), macrophage inflammatory protein-1 alpha (MIP-1 alpha), MIP-1 beta, and 1309) and two CXC chemokines (IL-8 and IP-10) were studied. Except for 1309, all CC chemokines induced chemotaxis of the NK cells in vitro, whereas the CXC chemokines were inactive. Maximal activity was obtained at 1 nM for MCP-1 and 10 to 100 nM for the other CC chemokines. The response showed a typically bimodal concentration dependence in all cases, except for RANTES, which induced a linear increase of migration over the concentration range of 0.1 to 1000 nM. A transient rise of the cytosolic-free Ca2+ concentration ([Ca2+]i), which is characteristic for chemokine-stimulated leukocytes, was observed in NK cells after stimulation with all six active chemokines. Since granule exocytosis is required for NK cell-dependent target killing, the effect of CC chemokines on exocytosis was tested. All CC chemokines that induced chemotaxis and [Ca2+]i changes also induced the release of granzyme A and N-acetyl-beta-D-glucosaminidase from cloned and blood NK cells, as well as CD8+ T cells after pretreatment with cytochalasin B. Maximum release was obtained from NK cells, and amounted to 35% and 13% of the total content of granzyme A and N-acetyl-beta-D-glucosaminidase, respectively. The capacity of cloned NK cells and CD8+ T cells to respond to chemokines depended on the time in culture after stimulation with PHA in the presence of irradiated feeder cells, and maximum responses were observed after 10 to 16 days. Our results demonstrate that CC chemokines activate NK cells, and are, therefore, not only attractants for monocytes, T lymphocytes, and eosinophil and basophil granulocytes.