Augmentation of cytotoxic activity by combination with interleukin 2 and interferon gamma

The synergy of cytotoxic activity by interleukin 2 (IL-2) and interferon gamma (IFN-gamma) was evaluated in human peripheral blood mononuclear cells (PBMC) and spleen cells. PBMC incubated with IL-2 (10 IU/ml) and IFN-gamma (200 IU/ml) for 4 days showed the stronger cytotoxic activity against K562, MOLT-4 and Daudi cells. Combination with IL-2 and IFN-gamma induced stronger activity than IL-2 or IFN-gamma alone. In order to investigate the sequential roles of IL-2 and IFN-gamma in the killer cell function, the cells were stimulated with IFN-gamma after washing of IL-2 or stimulated by IFN-gamma at various timing and duration without washing of IL-2. IL-2 was essential to induce the synergistic effect of IL-2 and IFN-gamma to cytotoxic activity. The similar augmentation of cytotoxic activity was observed by the addition of IFN-gamma at any incubation periods with IL-2, compared with stimulation with IL-2 or IFN-gamma alone. The phenotypes of the killer cells by stimulation with IL-2, IFN-gamma alone or IL-2 plus IFN-gamma were mainly CD2+, CD16+, indicating the activated natural killer cells.