Abstract: ObjectiveTo explore the role of L-arginine (L-Arg)in the treatment of breast cancer.MethodsThe experimental rodent model of breast cancer was prepared by injecting 4T1 cell line into the right side body of the mouse.The mice in L-Arg group were orally treated with L-Arg(1.5 g/kg)for successive 20 days when the tumor could be detected with palpation.Tumor size and survival rate were dynamically monitored.The mice were sacrificed and the spleen cell suspension was prepared when the treatment ended.Fluorescence activated cell sorter (FACS)was used to detect the T subsets and macrophage.Enzyme-linked immunosorbent assay(ELISA)and Griess reaction were used to detect interferon-gama(IFN-γ),interferon-alpha (TNF-α),and nittric oxide (NO),respectively.ResultsCompared with the control,treatment with L-Arg could inhibit tumor growth,prolong survival time of the mice.Meanwhile,L-Arg treatment significantly increased the percentages of CD4⁺ T(26.53±4.25%),CD8⁺ T cells(15.65±0.78%)and macrophages(7.62±0.86%) compared with the control group(19.53±2.50%,8.78±1.15%,and 2.02±0.12%,respectively) of the spleen cells.The contents of IFN-γ(36.56±10.50 pg/ml),TNF-α(22.05±4.93 pg/ml) and NO(30.28±6.00 μM) levels in L-Arg group were also significantly higher than those of the control group(15.47±4.96 pg/ml,14.69±0.81 pg/ml,and 6.57±2.21 μM,respectively,in the spleen cell culture supernatant.ConclusionL-Arg enhances T cell mediated immune response against tumor in the mice with experimental breast cancer.