IL-17 is a cytokine produced by various type cells.Previous studies have shown that IL-17 plays a critical role in the pathogenesis of diseases.However,less study has addressed the source of IL-17 and its mechanism in the development of allograft rejection response.Here we found that IL-17 expression was obviously up-regulated at the early stage of cardiac allograft rejection.These IL-17 are predominantly produced by CD3+ T cells,whereas IL-17 is rarely expressed by CD11c,CD11b,and NK1.1 positive cells.Interestingly,CD3 positive γδT cells also contributed to IL-17 production,and DC maturation was following the early elevated IL-17 expression during the alloimmune response,and it was worth noting that blockage of endogenous IL-17 activity suppressed DC maturation and decreased inflammatory cytokines during acute allograft rejection.Furthermore,as expected,we found that recombinant IL-17 significantly up-regulated costimulatory molecules of bone marrow derived dendritic cells (BMDCs) in vitro,and IL-17-treated BMDCs showed an increased capacity to enhance T cell function.In conclusion,our data provide clear evidence that early elevated IL-17 contributes to allograft rejection through modulating DC function.