Effect of human recombinant interleukin 2 on natural killing of low density Percoll fraction cells.

Human recombinant IL-2 (R IL-2) was used to validate the ability of this lymphokine to increase NK cell activity. It was found that R IL-2 was able to augment the K562 lytic activity of phagocyte-depleted mononuclear cells of low density in a dose dependent manner. This phenomenon was detectable after 24 h of incubation. Low concentrations of R IL-2 were sufficient for the activation of natural killing when the incubation time was longer than 24 h. Furthermore, IL-1 exerted an additive effect on R IL-2 induced augmentation of natural killing after 24 h, but not after longer incubation periods. Lymphocyte culture derived (L) and R IL-2 had similar effects on the K562 cytolytic potential of cells contained in low density fractions. The highest cytolytic activity was observed when Leu11a+ cells were incubated with IL-2. IL-2 induced K562 cytolytic activity was also seen after incubation of low density Leu11- cells for 48 h, 72 h, or 7 days. In cultures of low density Leu11- cells incubated with IL-2 for 7 days, a proportion of cells became Leu11+. From these findings we conclude that low density Leu11- cells are pre-NK cells which acquire natural killing potential under the influence of IL-2.