Abstract: Objective   To observe the expression of indoleamine 2,3-dioxygenase （IDO） in mouse bone marrow-derived dendritic cells （DCs） after adding Echinococcus granulosus recombinant antigen B （rAgB） in vitro.  Methods  CD11c⁺ DCs generated from bone marrow precursor cells of C57BL/6 mice and cultured in the presence of recombinant mouse GM-CSF （rmGM-CSF）. The morphology of DCs was observed by inverted microscope and scanning electronic microscope. The level of IA/IE，CD40，CD80，and CD86 on DCs were determined by flow cytometry. T cell proliferation induced by DCs were evaluated by using mixed lymphocyte reaction （MLR） assay. At day 6 postculture, the immature DCs were collected, and part of the immature DCs stimulated with lipopolysaccharide （LPS） for 24 h were examined by flow cytometry. Immature DCs were divided into 3 groups: negative control group，positive control group （rmIFN-γ，1 000 U/ml） and rAgB group. Immature DCs of positive control group and rAgB group were induced with 1 000 U/ml rmIFN-γ and 15 μg/ml rAgB，respectively. IDO expression in DCs was examined 24 h after induction using immunohistochemical method and Western blotting.  Results   More than 80% CD11c+ DCs were harvested. The typical DCs were observed under inverted microscope and scanning electronic microscope. The level of CD40， CD80， and IA/IE（MHCⅡ） in mature DCs group was significantly higher than that of immature DCs group （P<0.05）. In MLR，mitomycin-treated DCs can stimulate T lymphocytes proliferation activity. There were significantly differences in IDO expression in the negative control group ［（4.544±1.752）%］， positive control group ［（20.464±4.452）%］ and rAgB group ［（11.148±1.966）%］ （P<0.05）. Western blotting result indicated that the ratio of IDO/GAPDH in rAgB group （0.573±0.129） was significantly higher than that of negative group （0.229±0.085） （P<0.05）, and there were no significant difference in the ratio of IDO/GAPDH between IFN-γ group （0.794±0.114） and rAgB group （P>0.05）.   Conclusion   rAgB can induce IDO expression in bone marrow-derived dendritic cells in vitro.

Key words: Echinococcus granulosus recombinant antigen B, Dendritic cells, Indoleamin 2,3-dioxygenase, Immune tolerance