Estradiol promotes IFN-γ production by iNKT cells following in vivo IL-12/IL-18 challenge. Sham-operated (▪) and either placebo- (□) or E2-treated (▨) ovariectomized (Ovx) female mice received or not a single intravenous injection of IL-12 plus IL-18 and were killed 90 minutes later. Two separate experiments each including 3 mice per group are considered. (A) Serum IFN-γ concentrations are expressed as means ± SEMs. ^*P < .01; ^**P < .005. (B) Total liver mononuclear cells were analyzed in the αβ-TCR⁺ NK.1.1⁺ cell gate for IFN-γ synthesis by intracytoplasmic staining (bold line). As controls, cells were stained with irrelevant isotype-matched anti-IgG mAb (thin line). Mean percentages of IFN-γ–positive cells among iNKT cells: 45.6 ± 2.7 for sham-operated mice, 27.0 ± 2.0 for placebo-treated Ovx mice (P < .05 versus sham-operated mice), and 64.6 ± 4.0 for E2-treated Ovx mice (P < .01 versus placebo-treated mice). The proportion of IFN-γ–positive cells in the αβ-TCR⁺ NK.1.1⁺ gate was less than 0.5% in mice injected with vehicle alone.