The Function And The Mechanism Of Myeloid-derived Suppressor Cells In Inducing Immunosuppression In Transplantation

Transplantation is the best method for treating the end stage of organ failure diseases. About 300,000 patients suffered from organ failure are waiting for transplantation every year. The key problem in the field of transplantation is rejection of different types which is the influencing factor of surviving time of patients. Although completed check and immunosuppressive therapy was made for every single patient, rejection is still unavoidable. Rejection after kidney transplantation can be divided into hyperacute rejection, accelerated rejection, acute rejection and chronic rejection according to the time of occurrence. The most common type is acute rejection, and it is very important to prevent, diagnose and treat acute rejection.Myeloid-derived suppressor cells are a group of immature heterogeneous precursors of macrophages, granulocytes, dendritic cells and myeloid cells. These cells expand under the pathological condition of tumor, inflammation, autoimmune diseases, and infection with a strong immunosuppress fuction which were thought to be a potential method of immunosuppressive therapy in transplantation. The suppressive mechanisms of MDSCs are related to the upregulation of Arginase1(Arg1), inducible nitric oxide synthase(i NOS), heme oxygenase-1(HO-1), increasing radical oxygen species(ROS) in microenvironment, inducing regulatory T cells, inhibiting CD8+ T cells migration and apoptosis of CD8+ T cells. However, MDSCs also have the potiental ability in facilitating differentiation of TH17 cells under some conditions. Although there were a number of researches focus on MDSCs and transplantation, few of them noted the relationship of acute rejection and MDSCs, and it is stillcontroversial about the MDSCs’ ability of promoting TH17.Aim:(1) To study the change of MDSCs in patients who suffered from acute rejection after kidney tranplantation.(2) To investigate the influence of Arg1 on MDSCs in acute rejection model.(3) To explore the usage of MDSCs in inducing immune tolerance.Method:(1) Collecting the clinical data and peripheral blood of the patients who suffered from acute rejection after kidney transplantation, and analyzing the change of MDSCs with flow cytometry.(2) Using MHC mismatched skin graft model of Arg1 Mye KO mice, Arg1 conditional knockout as a mean to study the influence on MDSCs and graft rejection.(3) Using MHC mismatched skin graft model to study the usage of cultured MDSCs in vitro in transplantation tolerance.Result:(1) Acute T cell mediated rejection after kidney transplantation increased MDSCs level in PBMC significantly(p<0.0001), but have no influence on plasma IL-17 A level(p>0.05).(2) MDSCs infiltrated in allograft in acute rejection after kidney transplantation.(3) Arginase-1 deficiency prolongs the survival of murine skin allograft in MHC mismatched model(p<0.01), and DST cannot induce MHC mismatched skin grafts to survive longer(p>0.05). Skin transplantation increased the frequency of MDSCs in PBMC in both of B6 and Arg1 Mye KO mice at 5th day after skin transplantation(p<0.05) and decreased to the level before operation(p>0.05), and there was no significant difference between 2 groups at the same time point(p>0.05). The percentage of MDSCs in splenocytes did not change and could suppress T cell proliferating significantly in vitro(p<0.05), the suppress function in both group had no significant difference(p>0.05). Ten days post skin transplantation, the percentage of CD3+CD8+ T cells in splenocytes in both group increased significantly(p<0.05) in the same level(p>0.05). At 10 th day post skin transplantation, the percentage of CD3+CD4+ and CD3+CD8+ T cells decreased compared with that at 5th day in Arg1 Mye KO mice’s draining lymph node(p<0.05). The frequency of TH17 in draining lymph node had no significant difference between 2 groups(p>0.05). Skin transplantation increased the frequency of Treg in PBMC in both of B6 and Arg1 Mye KO mice at 5th day after skin transplantation(p<0.05) and decreased to the level before operation(p>0.05) and there was no significant difference between 2 groups at the same time point(p>0.05), and there was no change of Treg in spleen and draining lymph node(p>0.05). IL-17 A level was lower in Arg1 Mye KO mice’s serum than that in B6 WT at 5 days post transplantation(p<0.05); q RT-PCR showed that splenocytes of Arg1 Mye KO mice upregulate the expression of Inos,but downregulate the expression of Ifng, Rorc and Il17 a at 10 days post skin tranplantation(p<0.05). Paraffin section and flow cytometry of graft showed MDSCs infiltrated in skin allograft.(4) MDSCs were induced from bone marrow of B6 WT and Arg1 Mye KO mice using GM-CSF and IL-6, in both of them had a comparable suppressive activity in vitro, however, adoptive transfer of these MDSCs could not prolong the graft survival in MHC mismatched model(p>0.05).Conclusion:(1) Acute rejection after kidney transplantation increased MDSCs in PBMC;(2) Conditional Arg1 deficiency could prolong the survival of skin allograft, the mechanism might be related with the upregulating of Inos expression in Arg1 Mye KO MDSCs and their inhibitingthe expression of inflammatory factors of T cells.(3) Splenocytes from conditional Arg1 knockout had increased expression of Inos, but decreased expression of Ifng, Rorc and Il17 a.(4) MDSCs could infiltrate in graft after acute rejection;(5) Induced MDSCs from bone marrow had immune suppressive function in vitro, but could not prolong the survival of skin allograft after transferring.