Abstract: 【Abstract】 Objective  To determine the accumulation of CD11b+ Gr-1+ myeloid-derived suppressor cells（MDSC） in Schistosoma japonicum-infected mice.  Methods  Twenty-four C57BL/6 mice were infected cutaneously with S. japonicum cercariae. Peripheral blood samples were collected at 1, 2, 6 and 8 weeks post-infection （6 mice for each group）. At 6 and 8 weeks post-infection, spleens were removed and a single-cell suspension was prepared. At the same time, 6 healthy mice each served as control. During the different stages of infection, the levels of MDSC, Gr-1+ cells, CD11b+ cells in murine peripheral blood and spleen were detected by flow cytometry. The possible function of MDSC on T cells was evaluated by using a CCK-8 method and CFSE proliferation assay.  Results  At 6 and 8 weeks post-infection, the levels of MDSC （38.2%-57.8% and 47.1-77.6%， respectively）, Gr-1+ cells （28.9%-44.6%，40.4%-72.9%）, and CD11b+ cells （36.0%-48.1%，40.3%-68.3%） in infection group were significantly higher than that of the controls（15.1%-20.4%， 8.4%-17.3%， 9.8%-22.6%）, and that of infection group at 1 week （16.2%-19.8%， 13.0%-16.8%， 17.6%～19.4%） and 2 weeks （19.8%-29.5%， 17.2%-22.2%，20.9%-33.3%） post-infection （P＜0.01）. No significant difference was found in the levels of MDSC, Gr-1+ cells, CD11b+ cells among infection group at 1 and 2 weeks post-infection and control group. Moreover, the fluctuation trends of these cells in the spleens of infected mice were similar to those cells in peripheral blood （P＞0.05）. Strikingly, the proliferation index of normal CD4+ T cells was significantly lower after co-culture with Gr-1+ cells isolated from infected mice.  Conclusion  Schistosoma japonicum infection induces higher level of MDSC in mice, and Gr-1+ cells isolated from the infected mice can significantly inhibit the proliferation of the normal CD4+ T cells.

Key words: Schistosoma japonicum, Myeloid-derived suppressor cell, Immune tolerance, Flow cytometry