Abstract: Objective To observe the effects and mechanisms of Lycium barbarum polysaccharide(LBP)alone and combination with 5-fluorouracil (5-FU) on S180 tumor bearing mice.Methods Mouse S180 cells were subcutaneously injected into right axillary region of the mice.Eighty mice were randomly assigned into control group,5-FU group,LBP group,and LBP combined with 5-FU(LBP + 5-FU)group.Tumor weight and tumor control rate were detected after the experiment.Lymphproliferation response was detected with methyl thiazolyl tetrazolium(MTT)method.Cytotoxicity of nature killer(NK)cells to tumor cells was measured by lactate dehydrogenase(LDH).Macrophage phagocytosis was detected with neutral red experiment;nitrogen oxide(NO)production was detected by Griess and tumor necrosis factor-alpha(TNF-α)in peripheral blood was inspected by enzyme-linked immunosorbent asay(ELISA).Results LBP inhibited S180 tumor growth.The tumor control rate was 38.7% in high dose LBP group.Lymphoproliferation response of midium or high dose of LBP alone and combination with 5-FU group increased significantly compared with 5-FU group(P<0.01).Compared with the control group,cytotoxicity of NK cells to tumor cell in low,midium,and high dose LBP group increased significantly,with the proportions of 46±6%,52±11%,and 63±10%,respectively.Compared with 5-FU group,the phagocytosis of macrophage,nitric oxide production and level of TNF-α in serum in high dose LBP combination with 5-FU group increased significantly(P<0.01).ConclusionThese results suggest that LBP combination with 5-FU decrease the immune system damage induced by 5-FU.LBP might be a potential adjuvant for chemotherapeutic drugs.