M-CSF and prostratin induced Mregs promote immune tolerance in transplanted mice through Arg-1 pathway.

OBJECTIVE: Regulatory macrophages (Mregs) are a group of heterogeneous macrophages. These cells could induce immunosuppressive effects through the expression of immune regulatory molecules and cytokines.

METHODS: The differentiation of Mregs was induced by treating bone marrow cells with M-CSF and prostratin in vitro. The cell-phenotypes and immunosuppressive function were determined by flow cytometry. Rt-PCR was employed to assess the mechanisms of Mregs. Skin grafted mouse model was used for in vivo validation.

RESULTS: Mregs induced by M-CSF + prostratin had a strong inhibitory effect on T cell proliferation and cytokines production. The phenotype of induced bone marrow cells changed towards Mregs. These Mregs could induce the differentiation of Tregs in vivo. Arg-1 expression in these cells were significantly upregulated. Inhibition of arginase (Arg) or arginine supplement significantly reversed the immunosuppressive function. In mice skin-grafted models, adoptive transfer of these Mregs significantly prolonged allograft survival. In mice models, Arg-1 expression significantly elevated on skin grafts cells and Tregs increased in graft tissues.

CONCLUSIONS: We successfully developed a Mregs-inducing protocol with the combination of M-CSF and prostratin in vitro. M-CSF + prostratin induced Mregs prevented mice skin graft rejection through upregulating the expression Arg-1.