IL-4 synergistically enhances both IL-2– and IL-12–induced IFN-γ expression in murine NK cells

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Abstract
Interleukin-4 (IL-4) is thought to influence T and natural killer (NK) cells by down-regulating T helper 1 (Th1)–type cytokines like interferon-γ (IFN-γ). While investigating IL-4 regulation of IFN-γ expression, we found that IL-4 synergized with IL-2 or IL-12 to enhance IFN-γ production and mRNA expression in spleen-derived, IL-2–cultured NK cells, as well as negatively sorted fresh DX5+/CD3- NK cells albeit at lower levels. The positive effect of IL-4 on IL-2–induced IFN-γ production was dependent upon signal transducer and activator of transcription 6 (Stat6) because this response was virtually abrogated in Stat6-/- mice. Notably, though, IL-12 plus IL-4 synergy on IFN-γ expression was intact in Stat6-/- mice. In exploring possible molecular mechanisms to account for the synergistic effects of IL-4 on murine NK cells, we found that IL-2 plus IL-4 stimulation resulted in a modest increase in tyrosine phosphorylation of Stat5, while IL-12 plus IL-4 treatment resulted in a more substantial increase in tyrosine-phosphorylated Stat4. Finally, to identify regions of the IFN-γ promoter that may be involved, NK cells from human IFN-γ promoter/luciferase transgenic mice were treated with cytokines. NK cells from proximal (-110 to +64) promoter region mice did not respond to cytokine stimulation; however, the intact -565 to +64 IFN-γ promoter responded synergistically to IL-2 plus IL-4 and to IL-12 plus IL-4 in NK cells. These data demonstrate a role for IL-4 in enhancing IFN-γ expression in murine NK cells that is partially dependent on Stat6 in IL-2 costimulation and completely independent of Stat6 in IL-12 costimulations. (Blood. 2003;102:207-214)