Experimental autoimmune myocarditis (EAM) in rats is a T-cell-mediated disorder, and the involvement of Th1/Th2 unbalance has been demonstrated. The induction of antigen-specific tolerance is critical for the treatment of EAM and maintenance of immune tolerance. IL-10 is a pleiotrophic immunomodulatory cytokine that functions at different levels of the immune response, so it has emerged as a promising therapeutic factor for the treatment of autoimmune/inflammatory diseases. This study was designed to explore the effects of IL-10 gene modified bone-marrow-derived immature dendritic cells (iDCs) on the in vitro and in vivo immune response to cardiac myosin in EAM. EAM was induced using the classic methods of cardiac myosin immunization on day 0 and day 7. 2 x 10(6)/per rat mature DC (mDC), immature DC (iDC), pcDNA3 transfected iDC, pcDNA3-IL-10 transfected iDC or PBS were injected intravenously for treatment 5 days after the first immunization. On day 21, transthoracic echocardiogram and HE staining were performed to detect the cardiac function and myocardial inflammation. Th1/Th2 cytokines were detected by ELISA and MHC-II molecules, costimulatory molecules were identified by flow cytometry. In vitro T lymphocyte proliferation assay and adoptive transfer of DCs were performed to determine the antigen-specific tolerance induced by IL-10 gene modified iDCs. IL-10 gene modified iDC-treated EAM rats showed improved cardiac function and reduced infiltration of inflammatory cell into myocardium. Serum cytokines data indicated lower Th1 while higher Th2-type responses were induced in the pcDNA3-IL-10-iDC-treated group, suggesting a Th2 polarization. Moreover, IL-10 gene modified iDCs down-regulated MHC-II and costimulatory molecules on the surface of splenocytes and inhibited the antigen-specific immunological responses towards cardiac myosin. Adoptive transfer of IL-10 producing DCs prevented EAM induction. IL-10 gene modified iDCs ameliorates EAM histopathologically and functionally. The underlying mechanisms may be related to the IL-10 induced Th2 polarization and down-regulation of MHC-II molecules and costimulatory molecules expression.