Natural killer (NK) cells are innate lymphocytes that provide cytokines critical for early host defense against pathogens. One subset of human NK cells (CD56(bright)) constitutively expresses the high-affinity interleukin 2 (IL-2) receptor and produces immunoregulatory cytokines. Here, we demonstrate that CD56(bright) NK cells are present in human lymph nodes and that endogenous T cell-derived IL-2, acting through the NK high-affinity IL-2 receptor, costimulates CD56(bright) NK cells to secrete IFN-gamma. Thus, adaptive immunoregulators influence innate cytokine production, which in turn may influence the developing antigen-specific immune response. These data show a dynamic interaction between innate and adaptive human lymphocytes and emphasize the importance of studying interactions between immune components to understand the immune response as a whole.