Effects Of Tolerogenic Dendritic Cells Induced By Curcumin On Renal Allografts In Rats

BackgroundKidney transplantation is an effective treatment for end-stage renal diseases. It is necessary to reduce rejection after transplantation for prolonging graft survival time. Although immunosuppressants are currently used mainly to inhibit the rejection, long-term immunosuppressive therapy may cause the occurrence of infectious diseases and malignancies. Therefore, more effective and safes method need to be explored to reduce the amount of or replace immunosuppressants.Recently, studies focus on the specific immune targets, including dendritic cells (DC) which are the most powerful antigen-presenting cells (APC). DCs play dual roles in organ transplant immunomodulatory. Those promote graft tolerance are called tolerance DC (tol DC), and those induce allograft rejection are called immunogenic DC. DCs in normal circumstances exist mainly as immature DCs, which have a low expression of MHC Ⅱ molecules as well as co-stimulatory factor (CD80and CD86), and subsequencely a lower ability to stimulate T cells. Therefore, the immature DCs are often considered to be the prototype of tol DCs.Curcumin, extracted from turmeric, has powerful anti-inflammatory effect. Recent studies suggest that curcumin can regulate the function of inflammatory cells such as DCs and T lymphocytes. In this paper, we used cultured rat DCs to research the effects of curcumin on DC phenotype. Mixed lymphocyte reaction (MLR) was used to observe the role of DCs treated by curcumin in T lymphocytes proliferation and activation. We established kidney transplantation model in rat to examine the effect of curcumin-treated DCs in kidney transplant and to explore its possible mechanism.MethodsCultured DCs derived from bone marrow of Wistar rat were divided into four groups including immature group (no treatment factors), curcumin group (given curcumin treatment), lipopolysaccharide (LPS) group (LPS stimulation) and curcumin+LPS group (curcumin treatment before LPS stimulation). Flowcytometry was used to detect the expression of CD11c, MHC Ⅱ, CD80and CD86. ELISA was used to detect the IL-12secretion in cell culture medium. MLR was used to examine the effect of DCs in each group on the proliferation of separated T cells drived from spleen of Lewis rat. Alloantigen-specific T cells collected after initial MLR were stimulated by DCs drived from Wistar and Fischer344rats respectively to observe the role of DCs from each group in the reactivity of alloantigen-specific T cell.We used Wistar rats as donors and Lewis rats as recipients to established kidney transplantation model. Recipients were divided into three groups including control group (no intervention factors), immature group (preoperative infusion of immature DCs) and curcumin group (preoperative infusion of curcumin-treated immature DCs). Renal pathological changes and graft survival time were observed in each group. The mature DCs separated from Wistar and Fischer344rats respectively were used to stimulate T lymphocytes separated from rats of curcumin group and normal Lewis rats for MLR.ResultsFlowcytometry showed that there is no significant difference in the expression rate of DC-specific maker CD11c between each group. LPS significantly induced expression of CD80, CD86and MHC Ⅱ in DCs (P<0.05), while curcumin can inhibit this effect (P<0.05). ELISA exhibited that LPS significantly stimulated IL-12secretion of DC (P<0.05), while curcumin can inhibit LPS-induced IL-12production (P<0.05).In primary MLR, the immature DCs and curcumin processing DCs exhibited weak ability to induce T cell proliferation. LPS can stimulate DCs to induce T cell proliferation; however, curcumin-treated DCs maintained the weak ability to induce T cell proliferation even in the case of the inflammatory stimulus (LPS). In a secondary MLR assay, immature DCs and curcumin-treated DCs can induce alloantigen specific T cells anergy. LPS-stimulated DCs can not inhibite proliferation of T cells in response to alloantigen. However, DC treated by curcumin before LPS stimulation still had the ability to induce T cell anergy.The pathological changes in the kidneys were significantly improved in immature group compared with control group at7d after kidney transplantation, and the improvement of the curcumin group more pronounced. In addition, graft survival time in immature group was significantly longer than that in control group, while the prolongation of survival time in curcumin group was more significant compared with immature group (P<0.05). Furthermore, the proliferative response of T cells to donor-specific antigen in rats of curcumin group was significantly weaker than that of normal rats (P<0.05).Conclusions1. Curcumin can maitain the immature phenotype of DCs which is resistant to the inflammatory stimulus (LPS) induced mature.2. Curcumin-treated DCs can inhibit the proliferation of T cells and the induction of alloantigen-specific T cell anergy.3. Curcumin-treated DCs are tolerant to the pro-mature signals in vivo, thereby reduce rejection after transplantation and prolong graft survival time by inducing the tolerance of T cells to donor specific antigen.