IFN-γ upregulates IL-15 expression. The membrane and cytoplasmic forms of IL-15 were evaluated by FACS analysis. Human peripheral blood monocytes (A) and MONO-MAC-6 cells (B) were treated with IFN-γ, LPS, or LPS + IFN-γ or left untreated and were stained with the M112 MoAb as described in Materials and Methods. The mean ± SD from three independent experiments is shown. Significance was analyzed by comparison between treated and untreated cells with z-test (*P < .001). (C) cDNA derived from MONO-MAC-6 cells incubated for 6 hours with medium alone or supplemented with IFN-γ, LPS, or LPS plus IFN-γ were amplified with primers specific for IL-15. β-actin served as the control.