IL-17A but not IL-17F reduces NK cell cytotoxicity in vitro. Splenic NK cells were incubated with the indicated cytokines for 48 h before flow cytometric analysis of NK cells expressing granzyme B, perforin, or IFN-γ. Shown are results representative of two independent experiments. Data represent means and SEM values. **, P < 0.01; and ***, P < 0.001 versus IL-4 by one-way analysis of variance.