The Function And The Mechanisms Of Tregs In DST Induced MHC-I Mismatched Mouse Skin Plus Heart Transplantation Tolerance

At present, organ transplantation is the best method to end-stage organ failure. Althoughthe application of many kinds of new immunosuppressive drugs and tolerogenic inductionagent can be effective in the ratio of acute rejection decrease, various types of graft rejectionafter organ transplant are still impact the long time survival of graft. Therefore, how to induceand maintain immune tolerance, have become the focus in the field of transplantationimmunology.Regulatory T cells (Tregs) is one kind of special T cells subset. Because of theestablishment and maintenance of the stability of internal environment, and the function ofestablishment and induction of peripheral immune tolerance, Tregs cause for greatest concern.Various types of cells expressed this cell surface glycoprotein, CD47(integrin-associatedprotein, IAP). CD47as “self marker” express on hematopoietic cells. Especially in the fieldof immune tolerance induction, DST expressing CD47can induce persistent donor specifictolerance. However, there is not so clear that the role of Tregs in tolerance induction by DST.Aims:(1) To establish MHC-I mismatched mouse skin plus heart transplantation model;(2) To evaluate of the function and mechanisms of Tregs in MHC-I mismatched mouse skinplus heart transplantation tolerance induction by DST.Methods:(1) Using MHC-I mismatched skin plus heart transplantation model, DSTinduced skin and heart grafts tolerance as means to establish MHC-I mismatched mouse skinplus heart transplantation tolerance induction by DST.(2) Using MHC-I mismatched skin plusheart transplantation model, DST induced skin and heart grafts tolerance as means to evaluatedistribution, number, ratio and function of Tregs.Results:(1) In the MHC-I mismatched condition, heart grafts have long time survival inheart transplantation model, but skin grafts can rejected by donor in skin transplantation model (MST=15days). Interestingly, skin grafts can induce heart grafts rejection which fromthe same donor (MST=16.5days). In MHC-I mismatched skin plus heart transplantationmodel, the survival time of skin grafts in skin plus heart group (MST=16.5days) can beextend significantly compared to the skin only group (p<0.05).(2) In DST induce MHC-Imismatched skin plus heart transplantation tolerance model, the survival time of skin grafts inCD47+/+DST group (MST=46.5days) have been significantly prolonged compared to theskin grafts in Non-DST group (MST=17.5days, p<0.001), but CD47-/-DST can not increasethe survival time of skin grafts (MST=20days). The survival time of heart grafts inCD47+/+DST group (MST=42.5days) have been significantly prolonged compared to theheart grafts in Non-DST group (MST=15.5days, p<0.001), but CD47-/-DST can not increasethe survival time of heart grafts (MST=17days). CD86and I-Ab as activation markerexpression on host DCs can be up-regulated by CD47-/-DST, and the percentages ofCD11chiCD86+DC and CD11chiI-AbhiDC in total splenic CD11c+DC increased significantly.Furthermore, more effective T cells and Tregs can be observed infiltrated in heart grafts inCD47-/-DST group. And the area of infiltration of effective T cells and Tregs are the same.Contrary to CD47-/-DST group, no effective T cells and Tregs can be observed in tolerancedheart grafts. The number of Tregs in spleen and lymph nodes increased significantly18daysafter transplantation in CD47-/-DST group, but the ratio of Tregs in lymphocytes of spleenand lymph nodes decreased significantly. Compared to the number of Tregs in spleen, thenumber of Tregs in lymph nodes increased significantly18days after transplantation inCD47+/+DST group, but the ratio of Tregs in lymphocytes of spleen and lymph nodesincreased significantly.(3) In DST induce MHC-I mismatched skin plus heart transplantationtolerance model, anti donor T cell response increased significantly in CD47-/-DST group atthe time points of7days and14days after transplantation. But no anti donor T cell responsecan be observed in CD47+/+DST group. Furthermore, there are the same anti third party Tcells response in both CD47+/+DST and CD47-/-DST groups. There were no significantdifference of suppressive function of Tregs in both CD47+/+DST and CD47-/-DST groups.Conclusions:(1) In MHC-I mismatched condition, heart grafts have long term survival,but skin grafts can be rejected by donor, and skin grafts can induce heart grafts rejection. Furthermore, the volume of grafts effect the survival time of grafts.(2) DST expressing CD47can induce MHC-I mismatched skin and heart grafts tolerance, but DST losing CD47can notinduce tolerance. DST expressing CD47can inhibit donor DCs maturity, but DST losingCD47can induce donor DCs activation. At the time point of rejection, mass effective T cellsand Tregs infiltrated in grafts with parallel relationship. The number of Tregs in the lymphoidorgan of the donor with rejected increased, but the ratio of Tregs decreased. The number ofTregs in the lymphoid organ of the donor with tolerance increased a little bit, but the ratio ofTregs increased significantly. DST expressing CD47can induce recipient T cells anergy todonor antigen, but the suppressive function of Tregs in both CD47+/+DST and CD47-/-DSTgroups were the same.Significance: This subject expounds the role of Tregs in the transplant immune tolerancefrom another point of view, further improve the understanding of this sepecial kind of T cellsubsets, provides a new idea of tolerance induction program for clinical organ transplantation.