Soluble Fibrinogen-like Protein 2 Regulates Myeloid-derived Suppressor Cells Differentiation and Enhances Its Immunosuppressive Function of in Allograft Immunity

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Soluble fibrinogen-like protein 2 (sFGL2) is a novel immunoregulatory molecule, secreted mainly by regulatory T cells. CD11b+ Gr1+ myeloid-derived suppressor cells (MDSCs) are an important regulatory innate cell population and have significant inhibitory effect on T cell-mediated responses. Here, we synthesized murine full length sFGL2 by eukaryotic expression system, and investigated the impact on differentiation and function of MDSCs. Bone marrow cells from BABL/c mice were cultured with or without 10 μg/ml sFGL2 for 3 days and 5 days under 10 ng/ml GM-CSF stimulation. Compared with PBS, sFGL2 significantly induced CD11b+Ly6G-Ly6Chigh MDSC (MO-MDSC) differentiation but inhibited CD11b+Ly6G+Ly6Clow MDSC (PMN-MDSC) differentiation. The sFGL2-induced MO-MDSCs significantly inhibited T cells proliferation compared with those induced by PBS. Besides, sFGL2-induced MO-MDSCs demonstrated higher expression of arginase-1 and iNOS at both mRNA and protein level. Furthermore, adoptive transfer sFGL2-induced MO-MDSCs prolonged the skin allograft survival in mice. In the sFGL2-induced MO-MDSCs infusion group, the transplanted skin allograft showed mild inflammatory immune cell infiltration, less apoptosis and necrosis, and lower pro-inflammatory cytokines expression. T cells in the recipient mouse displayed a lower autoimmune phenotype (lower TCR+ CD44high CD62low cells). Taken together, our results indicate sFGL2 prompts MO-MDSCs differentiation and enhances their immunosuppressive function. National Natural Science Foundation of China.

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