UNLABELLED

Efficient induction of functional competent myeloid-derived suppressor cells (MDSCs) will be critical for the clinical application of MDSCs to treat autoimmune diseases and to induce transplantation immune tolerance. In the present study, we tried to establish the MDSC induction system with M-CSF and tumor necrosis factor α (TNFα) and investigated the immunosuppressive function of M-CSF + TNFα-induced MDSCs in transplant mouse models. Monocytic MDSCs (M-MDSCs) were induced by culture of the non-adherent mouse bone marrow cells with M-CSF or M-CSF + TNFα, respectively, for 7 days. Phenotype analysis revealed that the majority of M-CSF- and M-CSF + TNFα-induced MDSCs express F4/80. The addition of TNFα in the induction period increased Gr-1, Ly6C, CD80, and CD274 expressions on these cells. M-CSF + TNFα-induced M-MDSCs showed poor TNFα, IL-12, and IL-6 expressions after lipopolysaccharide (LPS) stimulation and decreased arginase 1 (Arg-1) and Fizz expressions after IL-4 stimulation compared with M-CSF-induced M-MDSCs. M-CSF + TNFα-induced M-MDSCs showed enhanced ability to suppress T cell proliferation and cytokine production than M-CSF-induced M-MDSCs. M-CSF + TNFα-induced M-MDSCs express high levels of inducing nitric oxide synthase (iNOS) and blocking iNOS activity by a chemical inhibitor or gene deficiency significantly reversed the inhibitory effects of M-CSF + TNFα-induced M-MDSCs on T cells. Adoptive transfer of M-CSF + TNFα-induced M-MDSCs promoted immune tolerance in a male-to-female skin-grafted mice, but M-CSF + TNFα-induced iNOS-deficient M-MDSCs failed to do so. Thus, M-CSF + TNFα-induced M-MDSCs have powerful immunosuppressive activity, which is mediated by an iNOS-dependent pathway. M-CSF + TNFα-induced M-MDSCs can promote immune tolerance to donor antigens in a transplant mouse model.

KEY MESSAGE

The combination of M-CSF and TNFα efficiently induces functional M-MDSCs in vitro. M-CSF + TNFα-induced M-MDSCs promote immune tolerance in a transplant mouse model. The immunosuppressive ability of M-CSF + TNFα-induced M-MDSCs is dependent on iNOS.