Figure 4.

MDSCs inhibit T cell proliferation via IL-10 and arginase-1 in vitro. (A) Monocytes and MDSCs (CD11c-CD11b+ GR-1+ cells) were obtained from CIA mice at five weeks after induction of CIA. The mRNA levels of various immunoregulatory molecules including FcγRIIB (CD32), IL-10, iNOS, PDL-1, PDL-2, and arginase 1 were measured using real time PCR. *P < 0.05, **P < 0.01, ***P < 0.001. (B) T cells isolated from CIA mice were cultured for 72 hours in medium alone, with MDSCs, or monocytes (at 1:1 ratio) obtained from CIA mice as described in Materials and Methods section. The degree of apoptosis was assessed by flow cytometry using propidium iodide (PI) and Annexin V. Apoptotic cells were defined as PI-Annexin V+ cells. Representative results from three independent experiments are shown in the left panel. The percentage of apoptotic T cells is shown in the right panel. *P < 0.05. (C) T cells were cultured with MDSCs (at 1:1 ratio) for 72 hours in the presence or absence of anti-IL-10 (10 μg/ml), anti-TGF-β (10 μg/ml), L-NMMA (500 μM), nor-NOHA (500 μM), anti-FcγRIIB (2 μg/ml), or anti-PDL-1 (5 μg/ml). T cell proliferative responses were determined by [³H]thymidine incorporation assay. *P < 0.05.