Dexamethasone Prolongs Cardiac Allograft Survival in a Murine Model Through Myeloid-derived Suppressor Cells

Background. Recently, myeloid-derived suppressor cells (MDSCs) have attracted considerable attention because of their cancer-promoting and immunosuppressive effects. The glucocorticoid dexamethasone (Dex) is an important immunosuppressive agent used to treat autoimmune diseases and organ transplant rejection. However, the mechanism by which it modulates the immune system is not completely understood. Material and Methods. In this study, we investigated the mechanisms by which Dex modulated the immune response in mice given an allogeneic cardiac transplant. Results. Dex injection significantly prolonged heart graft survival compared with phosphate-buffered saline-injected controls. Dex treatment increased the number of splenic MDSCs. Moreover, Gr-1(high)/CD11b(+) MDSCs and CD3(+)/CD4(+)/Foxp3(+) regulatory T cells (Tregs) were significantly increased in the Dex group compared with controls. Administration of anti-Gr-1 antibody (Ab) to the Dex group significantly shortened mouse heart graft survival. In addition, anti-Gr-1 Ab treatment significantly reduced Tregs in the Dex + anti-Gr-1 co-treatment group compared with the Dex group. These observations suggest that Dex treatment increased both MDSCs and Tregs, and that MDSCs regulated the incidence of Tregs in this immunosuppressive pathway. Conclusion. An important role of Dex in the prevention of the rejection of cardiac grafts in mice is to expand MDSCs and Tregs.