Background Alveolar echinococcosis (AE) is caused by the metacestode stage of Echinococcus multilocularis (E.multilocularis) and is a rare but life-threatening disease.This disease commonly is characterized by an infiltrative,tumor-like growth of the E.multilocularis metacestode in the liver of human.Liver transplantation is an effective therapy for end-stage of hepatic AE,but the characteristics of host immunity associated with E.multilocularis infection with organ transplantation are poorly defined.We hereby aimed to study the immunological status and allograft heart survival in inbred rats with E.multilocularis infection.Methods Rat models of AE were established by injecting the E.multilocularis suspension made from E.multilocularis infected tissues into the abdomen of Lewis (LEW) rats.Three months later,in the experimental group,allograft heart transplantation was performed from Brown-Norway (BN) rats to the E.multilocularis infected LEW rats.In the control group,we transplanted hearts from BN rats to healthy LEW rats.The influence of the disturbed immune system in E.multilocularis infected rats on the heart transplantation was assessed,including observation of allograft heart survival time,histopathological examination of grafts and immunohistochemical examination of infiltrating cells (CD4+ T cells,CD8+ T cells and eosinophile granulocytes),measurement of interleukin (IL)-4 and interferon (IFN)-Y in the serum by enzyme-linked immunosorbent assay (ELISA) and analysis of CD4+CD25+ regulatory T cells in peripheral blood by fluorescence activated cell sorting (FACS) flow cytometric analysis.Results The survival time of recipients in the experimental group was prolonged compared with those in the control group.The numbers of graft infiltrating CD8+ T cells were decreased whereas the graft infiltrating eosinophil granulocytes (CD15+) were increased in grafts in the experimental group (P ＜0.05).Furthermore,the proportion of CD4+CD25+ regulatory T cells in the peripheral blood was 10.8％ on average in the experimental group,which was significantly higher than that in the control group (6.1％).In addition,the level of serum IL-4 in E.multilocularis infected rats was higher than that in the control group rats,whereas the level of serum IFN-γ in experimental group was lower than that in the control group when graft rejection occurred (P ＜0.05).Conclusions This study suggests that E.multilocularis infection could prolong the allograft survival time through the polarization of Th1/Th2-type cells and induction of CD4+CD25+ regulatory T cells.This strategy may provide a new idea for establishing transplantation tolerance.