Enhancement of cytotoxic activity of natural killer cells by interleukin 2, and antagonism between interleukin 2 and adenosine cyclic monophosphate.

Two cytokines, interferon (IFN) and interleukin 2 (IL-2), activate murine natural killer (NK) cells in vitro. Together both factors synergize considerably. Antibody against IFN eliminates the response of NK cells to IFN as well as to IL-2, whereas antibody against IL-2 blocks the effect of IL-2 but not of IFN. These findings as well as previous observations imply that both factors act on the same cell but have different roles. We suggest that IFN induces NK cell activation and IL-2 enhances this effect. Further studies revealed that besides inducing cytotoxicity in NK cells IFN induces the production of prostaglandin E (PGE) which inhibits NK cell activation. We propose therefore that IFN has a dual effect on NK cells: it induces NK cells to become cytotoxic and initiates a negative feedback by increasing the production of PGE. IL-2, which synergizes with IFN in the activation of NK cells, ceases to do so when the negative feedback (PGE-mediated) is blocked with indomethacin. We infer that IL-2 enhances NK cell activity by interfering with the negative feedback rather than by aiding NK cell activation.