Objective: To investigate how gene silence of CD40 by siRNA influences the balance of Th1/Th2 and Th17/Treg in rats with experimental autoimmune myocarditis(EAM).Methods: Lewis rats were divided into normal-control group,EAM group,CD40siRNA-therapy group and siRNA-control group,using random number table.EAM,CD40siRNA-therapy and siRNAcontrol group were immunized on day 0 and day 7 with purified porcine cardiac myosin to establish EAM,and CD40siRNA was administered intravenously on day 7.The basic information of each group was observed,and the rats were executed on day 21 to study The pathology of myocardial tissue and calculate the myocardial histopathology scores,after the changes of electrocardiograms(ECG)and echocardiogram were recorded.Enzyme linked immunoabsorption assay(ELISA)was used to determine the level of interferon(IFN)-γ,interleukin(IL)-10,IL-17 and transforming growth factor(TGF)-β in peripheral blood.Result: s(1)The overall incidence of EAM,CD40siRNA-therapy and siRNA-control group was 100%,and no one died from day 0 to day 21.(2)There was only 2 premature beats in EAM and siRNA-control group,while the ECGs of normal-control group and CD40siRNA-therapy group were normal.(3)The echocardiogram of EAM,CD40siRNA-therapy and siRNA-control group,displayed left ventricular dilatation,hypertrophy of left ventricle,weaken of left ventricular wall motion,and heart failure,and pericardial effusion was discovered.Left ventricular fractional shortening(LVFS)and left ventricular ejection fraction(LVEF)of rats treated by CD40siRNA were higher than those of rats of EAM group[(46.70±8.25)%vs.(34.28±11.81)%,(80.92±11.76)%vs.(64.03±12.60)%,F=0.652,0.234,P<0.05].(4)Pathologic examination of EAM group,CD40siRNA therapy group and siRNA control group,showed myocardial fiber fracture,myocardial tissue necrosis and inflammatory cell infiltration.But myocardial tissue pathological score of cardiac tissue of CD40siRNA therapy group was lower than that of EAM group(2.10±1.07 vs.3.40±0.72,F=1.290,P<0.05).(5)ELISA Methods,examination revealed that the levels of every cytokines in EAM group rose [(1245.55±244.56)ng/L vs.(501.53±18.93)ng/L,(78.03±10.47)ng/L vs.(30.77±1.74)ng/L,(80.82±13.33)ng/L vs.(27.98±3.01)ng/L,(156.27±12.11)ng/L vs.(4.33±0.79)ng/L,F=4.346,3.833,6.644,5.051,P< 0.05].However,the levels of IFN-γ and IL-17 in CD40siRNA therapy group were lower than that in EAM group [(940.62±128.40)ng/L vs.(1245.55±244.56)ng/L,(60.42±12.40)ng/L vs.(80.82±13.33)ng/L,F=1.774,0.052,P < 0.05],while the levels of IL-4 and TGF-β were higher[(97.91±13.62)ng/L vs.(78.03±10.47)ng/L,(178.84±12.10)ng/L vs.(156.27±12.11)ng/L,F=0.019,0.009,P<0.05].Conclusion: Myocardial inflammation reduced and the cardiac functional recovery promoted by administering CD40siRNA,can be explaned by Th1-type and Th17-type cytokines inhibited,Th2-type and Treg-type cytokines increased,and so then the imbalance of Th1/Th2 and Th17/Treg corrected.