Natural killer (NK) cells mediate innate immune responses against infections and tumor metastasis. Human NK cell lymphoma NK92, an interleukin-2 (IL-2)-dependent cell line, is one of few cell lines with phenotype and functions similar to normal peripheral blood NK cells. NK92 may serve as a model for NK cell cytokine regulation studies. IL-2, IL-12 and IL-18 regulate NK cell cytokine production, but the mechanisms are not clear. Objectives: To understand the mechanisms of cytokine regulation in NK cells, using NK92 lymphoma as an in vitro model. Methods: We examined kinetics of TNFa and IFNg mRNA expression in response to several cytokines, including IL-18. NK92 subclones were IL-2-starved for 13 hours, then incubated in culture medium alone, or with IL-2, IL-2+IL-12, IL-2+IL-18 or IL-18 only, for 2, 8 or 24hrs. Total RNA was purified using TRI-Reagent (MRC, Cincinatti, OH), and TNFa, GM-CSF, IFNg, and IFNg receptor expression was analyzed by RNase protection assay (RPA) using an RPA kit with ³²P-labeled probes synthesized on custom template set (BD Pharmingen, San Diego, CA). Band signal was quantitated by phosphoimaging. Results: Consistent with previous studies, IL-2 alone, or combined with IL-12 or IL-18, up-regulated TNFa and IFNg mRNA expression by 2hrs (earliest measured). IL-2+IL-12 was the strongest stimulus. TNFa mRNA declined more sharply, than did IFNg. However, IL-18 alone had little effect on TNF a, and little to no effect on IFN g mRNA expression. These results differ from those reported by U. Kalina, et al. (J. Immunol. 2000, 165:1307), which could be explained by different experimental conditions. Conclusion: IL-18 alone may not be sufficient to stimulate NK92 IFNg production. This may be physiologically relevant, since IL-18 is expressed in various tissues. IFNg is a potent proinflammatory cytokine that requires tight regulation to prevent unnecessary damage. Supported by NIH/NIDCR P30 DE10126 and by UI Dental Research Award.

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