Fig. 2.

NK cells secrete high levels of immune stimulatory cytokines following FcR activation in the presence of IL-12. a Human NK cells were stimulated via their FcR by culture onto wells pre-coated with either huIgG or Ab-coated SK-BR-3 tumor cells, or by direct FcR cross-linking by 3 g8 Ab. IL-12 was added at a concentration of 10 ng/mL. Control wells consisted of NK cells cultured with medium alone (medium), FcR activation alone (via immobilized huIgG, Ab-coated tumor, or 3 g8 cross-linking, as indicated), or IL-12 alone (IL-12). Culture supernatants were harvested after 12 h and analyzed for IFN-γ content by ELISA. In time-course experiments, NK cells were cultured onto immobilized huIgG with IL-12 for varying times (4-72 h) and supernatants were analyzed for (b) IFN-γ, (c) MIP-1α, and (d) TNF-α. The means and SEM are shown with n = 3 for each experiment. *p < 0.001 vs. Medium, FcR activation alone, and IL-12 alone. e NK cells cultured in the immobilized IgG plus IL-12 condition were harvested at varying times and processed for Real-Time PCR analysis of IFN-γ transcript. Results are given as fold increase in cytokine transcript over baseline (Medium). The means and SEM are shown (n = 3). *p < 0.01 vs. Medium, immobilized IgG, and IL-12. Similar results were observed for gene expression of MIP-1α and TNF-α (not shown)