Objective: To determine the accumulation of CD11b+ Gr-1+ myeloid-derived suppressor cells (MDSC) in Schistosorna 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.