Modulation of TfR expression by IFN-γ/LPS in J774 macrophages. Cells were stimulated for 16 hours (A) or 24 hours (B) with the indicated concentrations of IFN-γ (U/mL), LPS (ng/mL), and/or NMMA (500 μmol/L) and the expression of TfR determined by flow cytometry as described in the Methods. Nitrite production was assayed in the culture medium by the Griess reaction. Results shown are representative of 5 separate experiments. Values are given as the mean ± SE of triplicate cultures. Versus control: *P < .05, **P < .01; versus IFN: ^#P < .05; versus IFN/LPS: ^&P < .001.