The Function Of Myeloid-derived Suppressor Cells In Graft Tolerance After Mouse MHC-mismatch Liver Transplantation

Part I:The Role of Myeloid-derived suppressor cells in mouse liver transplantation【Objectives】 Myeloid-derived suppressor cell (MDSC) are a group of newly discovered myeloid cell populations which have shown a strong immune regulatory functions. The mechanisms in spontaneous graft tolerance phenomenon of murine allogeneic liver transplantation (LT) has not yet been well explained. Recent research has shown that MDSC can promote tolerance of transplanted mouse islet cells; however, the role of MDSC in immune tolerance after MHC-mismatched mLT still leaves unknown. The aim of our study is to discover the changes of lymphocyte in immune tolerance after MHC-mismatched mLT.【Methods】mLT was used in this study for in vivo study. The immune micro- environment changes and the fluctuation of MDSC and Tregs level in immune tolerance after MHC-mismatched mLT were observed.【Results】 A significantly immune micro-environment change was observed in mLT, especially in allogeneic LT; in the early period after LT (4weeks), a large number of lymphocytes infiltrated into the liver graft, cousing a serious destruction in graft; in tolerance period (8weeks), the infiltration of lymphocytes was significantly reduced; flow cytometry shown that number of MDSC and regulatory T cells (Tregs) increased marblely in MHC-mismatched mLT group; Also, a linear correlation between them was observed.【Conclusions】 After MHC-mismatched mLT, the number of infiltrating MDSC and Tregs increased substantially,the increase of MDSC was observed and having synergy with increased Tregs, suggesting that MDSC may regulator the immune tolerance after MHC-mismatched mLT by the adjusting the function of Tregs. Part Ⅱ:Mechanism of myeloid-derived suppressor cells in the spontaneous immune tolerance of mouse liver transplantation 【Objectives】 Spontaneous immune tolerance of mouse liver transplantation has been one of the hotspot in transplantation immunology, even though recent research indicates that regulatory T cells (Tregs), stellate cells and Kupffer cells play a certain role in the process, but the mechanisms are not clarified. The reason that why mouse liver transplantation could generate spontaneous immune tolerance will certainly be the key to a new strategy of immunosuppressive therapy in clinical liver transplantation. Myeloid-derived suppressor cells(MDSC) are a recently discovered heterogeneity population of immune cell, with strong immune moderate functions. The first part of our research showed that, the process of immune tolerance induction of mouse liver transplantation characterized by increased infiltration of MDSC, which shows a synergy with increased Tregs. These result indicated that, MDSC play an important role in the tolerogenicity of mouse liver transplantation. The negative immune regulation function of MDSC may have relationship with Tregs. In order to find the inner mechnisms of MDSCs midated immune-regulation, we comduct some experiments as shown below.【Methods】MDSC separated and purified from syngenic/allogenic transplanted mouse liver were co-cultured with wild type effector T cells, added with or without wild type Tregs into the culture system for72hours, then observe the inhibition effect on Teff cells and coordinate regulation with Tregs.Serum samples were collected for ELISA to valuate the serum level of IL-10, IL35and TGF-β. Micro RNA chip were used to found different gene expression levels in syngenic/allogenic transplanted mouse liver. The changes of MDSC related gene expression level were obtained by contrast the results of Micro RNA chip to Genbank and literature. 【Results】 MDSC can induce the death of Teff cells independent of Treg. But when MDSC inhibite the proliferation of Teff cells, the assist of Tregs is essential. The ELISA result show that the serum level of IL-10in allo-transplantation group is obviously higher than syn-transplantation group. Results of miRNA chip show that,188differences genes were found in this test; among them, there are10different genes may be relative with transplant immune regulation,some of them may invovel in TGF-β signaling pathway, resulting in negative regulation of the immune by MDSC.【Conclusions】 By promoting the death of Teff cells and inhibiting its proliferation with the help of Tregs, MDSC play an important role in the process of the spontaneous immune tolerance of mouse liver transplantation. IL-10may be the key cytokine that take part in the process of MDSC negatively regulate immune response and accommodate the function of Tregs. What's more, results of miRNA chip indicate that, some new gene like Ptpn23, Prkaa1, Oxsr1, Rlf, Pkn2, Aicda may also play an important role in the immune moderation function of MDSC.