Abstract：Objective: To study the regulatory mechanism of sildenafil on myeloid derived suppressor cells(MDSC) proportion in the peripheral blood and the changes of immune function in mice with gastric transplanted tumor. Methods： Mice were subcutaneously implanted with MFC tumor cells in the right back region.Eighteen female 615 mice aged six weeks were randomly divided into 3 groups: normal control group, tumor-bearing mice plus PBS group and tumor-bearing mice plus sildenafil group. The mice were transplanted with gastric tumor, after 24 hours,they were daily administered with sildenafil. Tumor-bearing mice plus PBS group were daily administered with the same volume of PBS.The antitumor activity of sildenafil was determined by calculating the tumor inhibitory rate. The proportion of MDSC and T lymphocyte subsets in peripheral blood were detected by flow cytometry. Results： Compared with normal control group,the proportion of MDSC in the peripheral blood was significantly increased(P<0.05), and the ratio of CD4+/CD8+in the peripheral blood was decreased(P<0.05) in mice with gastric transplanted tumor.The proportion of MDSC was negatively correlated to CD4+/CD8+ratio(r=-0.858,P<0.01). Compared with tumor-bearing mice plus PBS group, treatment with sildenafil could remarkably inhibit the tumor growth in mice with gastric transplanted tumor. After 28 days, the tumor inhibition rate was 41.2%. Moreover, the proportion of MDSC was decreased(P<0.05)，and the ratio of peripheral blood CD4+/CD8+ was increased(P<0.05). Conclusion： An increase of the proportion of MDSC in the peripheral blood may lead to abnormality of immune function in mice with gastric transplanted tumor. Sildenafil might enhance antitumor immunity response and inhibit tumor growth by restraining the proportion of Gr1+CD11b+ myeloid derived suppressor cells and regulating the proportion of T cell subsets.
2013, Vol. 23 
