Dose- and time-dependent upregulation of membrane IL-15 after IFN-γ treatment. MONO-MAC-6 were treated with the indicated amounts of IFN-γ for 24 hours (A). In (B), MONO-MAC-6 were treated with medium alone or with IFN-γ (500 U/mL) for the indicated time. Cells were then stained with M112 MoAb as described in Materials and Methods and were analyzed by FACS. Results represent mean ± SD of three independent experiments. Significance was analyzed by comparison between treated and untreated cells with the z-test (*P< .001).