Figure 5. DFMO impairs MDSC function by reducing arginase expression and activity.
(A) Real-time quantitative RT-PCR analysis of arginase-I expression in MDSCs from DFMO-treated and control mice (5 mice per group). Arginase-I activity of DFMO-treated MDSCs was compared with that of control MDSCs (3 mice per group). (B) Suppressive activity of DFMO-treated MDSCs versus control MDSCs. MDSCs were added at different ratios to eFluor450-labeled CD4+ T responder cells (Tres) stimulated with anti-CD3 plus antigen-presenting cells (APC) for 3 days and T cell proliferation was measured by flow cytometric eFluor450 dye dilution (3 mice per group). Arginase-I inhibitor nor-NOHA was able to blunt the suppressive activity of control MDSC but not DFMO-treated MDSCs. *, p<0.05; **, p<0.01. Data are representative of 3 independent experiments.