Immunosuppression is the main source of ineffective treatment on tumor, and the study aimed to investigate the effect of artesunate on tumor immunosuppression. Supernatants of re-cultivated murine colorectal cancer cell Colon26 and human colorectal cancer cell RKO after pre-treatment with or without artesunate were enrolled, and their effects on five immune parameters were assessed, including killing activity of natural killer (NK) and lymphocyte proliferation, as measured by MU, and expressions of interleukin 2 receptor (IL-2R)alpha, CD3 epsilon(+)zeta(+) and CD3 epsilon(-)zeta(+) on lymphocytes, as analyzed by flow cytometry. Six immunosuppressive factors were measured by ELISA, including transforming growth factor (TGF)beta(1), vascular endothelial growth factor (VEGF), IL-4, IL-6, IL-10, and prostaglandin E-2 (PGE(2)). Then, multiple linear regression analysis was applied to reveal the correlation between immunosuppression and immunosuppressive factors, and was used to confirm the findings. It was shown that Colon26 and RKO cells secreted immunosuppressive factors and inhibited these five immune parameters steadily. After pretreatment with artesunate, immunosuppression from the two cells was down-regulated significantly (all P < 0.05), and the concentrations of TGF-beta(1) and IL-10 decreased greatly (all P <0.001). There were positive correlations between the down-regulation of immunosuppression and the decrease in TGF-beta(1) or 1L-10. Their combined potency attributed to decreased TGF-beta(1) and IL-10 with respect to the down-regulating effect of artesunate on immunosuppression of NI( killing, lymphocyte proliferation and expressions of IL-2R alpha and CD3 epsilon(+)zeta(+), was about 60%-90%. The present analysis provides clues that artesunate reverses the immunosuppression from Colon26 and RKO colorectal cancer cells by decreasing TGF-beta(1) and IL-10. This is probably one of the anti-tumor mechanisms of artesunate. (C) 2015 Published by Elsevier B.V.