BACKGROUND: Immature dendritic cells (imDC) can prolong allograft survival in murine transplantation models. Recent data indicate that semi-mature or alternatively activated DC (aaDC) may be even more tolerogenic. METHODS: We compared the phenotype and regulatory capacity of: a) imDC, cultured in the presence of dexamethasone (DEX), b) mature DC (matDC), activated with LPS, and c) aaDC, activated with LPS after pretreatment with DEX. RESULTS: As compared to imDC, aaDCs displayed a slight upregulation of CD40 while expression levels of MHC-II and CD86 remained low. The production of proinflammatory cytokines, in particular IL-12, by aaDC was much lower than by matDC while both produced similar amounts of the regulatory cytokine IL-10 leading to an increased IL-10/IL-12 ratio for aaDC. After infusion of donor type aaDCs, responder cells isolated from the recipient mice showed donor-specific hyporesponsiveness to restimulation by matDC. Infusion of matDC was immunogenic, while imDC induced partial hyporesponsiveness. Importantly, pretreatment with donor type aaDC (but not imDC) resulted in prolonged survival of a completely MHC-mismatched heart allograft. CONCLUSIONS: Alternatively activated DC are more efficacious than the classical imDC in the regulation of the alloimmune response, which may be related to a distinct cytokine profile characterized by an increased IL-10/IL12 ratio.