Iron released by IFN-γ/LPS-activated J774 macrophages. Macrophages were incubated for 24 hours with 50 μg/mL⁵⁹Fe-Tf and then stimulated overnight with the indicated concentrations of IFN-γ (U/mL), LPS (ng/mL), and/or NMMA (500 μmol/L) in the presence of unlabeled Fe-Tf. Nitrite production was assayed in the culture medium by the Griess reaction. Results shown are representative of 3 separate experiments. Values are given as the mean ± SE of triplicate cultures. Versus control: *P < .05, **P < .001, ***P < .0001.