Abstract： Objective To study the effect of donor immature dendritic cells(imDCs)treated with Tacrolimus(TAC)on prolonging rat allograft survival and the action mechanism.Methods Cervical heart transplantations were performed in which Wister rats were used as donors,and SD rats as allograft recipients.Normal sodium(control group),imDCs(positive control group),and imDCs treated with TAG(TAC-treated group)were injected via vena caudalis 7 days before the operations respectively.Heart allograft survival was monitored and one-way MLR,heart pathology and the levels of IL-2,IL-4,IL-10,IFN-r in the serum were detected Results H test showed that there was high significant difference in heart allograft survival among the three groups(P＜0.01).Stimulation index in positive control and TAC-treated groups 2 and 3 in MLR was obviously lower than in control group,while stimulation index to independent donors in positive control and TAC-treated group were close to control group.Analysis of variance showed that there was high significant difference in serum concentrations of IL-2,IFN-r,IL-4,IL-10 among the three groups(P＜0.01).The concentrations of IL-2 and IFN-r being expressed on Thl were lower,and those of IL-4 and IL-10 being expressed on Th2 were obviously higher in positive control and TAC-treated groups.Conclusion ImDCs can prolong rat heterotopic cardiac allograft survival successfully;ImDCs treated with TAC can enhance the effect which is donor specific.ImDCs may induce the immune tolerance by means of modifying the immune response type of T cells(immune deflection from Th1 to Th2),and inducing T cells disenabling.