Abstract: 【Objective】 This study was aimed to investigate the effect of astaxanthin extracted and purified from Rhodotorula mucilaginosa on the immune function of immunosuppressed mice,so as to provide theoretical basis for the development and application of astaxanthin in the prevention of immunosuppressed diseases or as a substitute feeding product for livestock and poultry.【Method】 Astaxanthin was extracted from Rhodotorula mucilaginosa ZTHY2 isolated from the coastal waters of Leizhou Peninsula.Sixty C57BL/6 mice were randomly divided into 6 groups:Blank control group,cyclophosphamide group,yeast β-glucan group and astaxanthin low,medium and high dose groups.From 1-14 days,the mice in yeast β-glucan group were gavaged with 100 mg/kg yeast β-glucan,the low,middle and high astaxanthin groups were gavaged with 30,60 and 100 mg/kg astaxanthin,respectively,and the blank control and cyclophosphamide groups were intragastrically injected with normal saline.On the 15-21 days,except for blank control group (normal saline),the mice in each group were intraperitoneally injected with 50 mg/kg cyclophosphamide.At the end of the experiment,the spleen and thymus of mice were collected,and the organ index and the proliferation of T and B lymphocytes in spleen were calculated.The histological changes of spleen and thymus were observed.The contents of interleukin 2 (IL-2),IL-4,IL-6,tumor necrosis factor α (TNF-α),interferon gamma (IFN-γ),immunoglobulin A (IgA),IgG,IgM,CD4,CD8,CD19,CD20,glutathione (GSH) and malondialdehyde (MDA) in serum,the activities of catalase (CAT) and superoxide dismutase (SOD) in serum,and the level of reactive oxygen species (ROS) in spleen were determined.【Result】 Compared with blank control group,the spleen and thymus indexes of mice in cyclophosphamide group were extremely significantly decreased (P＜0.01),the boundary between red and white pulp of spleen was unclear,the number of spleen lymphocytes decreased,the thymus cortex and medulla were unclear,and the structure was destroyed.The proliferation ability of T and B lymphocytes in spleen was extremely significantly decreased (P＜0.01).The contents of cytokines IL-2,IL-4,IL-6,TNF-α,IFN-γ,CD4,CD8,CD19,CD20 and immunoglobulin IgA,IgG and IgM in serum were significantly or extremely significantly decreased (P＜0.05 or P＜0.01).The activities of CAT and SOD and the content of GSH in serum were extremely significantly decreased(P＜0.01),while the levels of MDA and ROS were extremely significantly increased (P＜0.01).Compared with cyclophosphamide group,the structure of spleen and thymus in astaxanthin group became clearer with the increase of astaxanthin concentration,and the spleen and thymus indexes were extremely significantly increased (P＜0.01).Astaxanthin could extremely significantly promote the proliferation of spleen lymphocytes induced by concanavalin A (ConA) and lipopolysaccharide (LPS) (P＜0.01).Astaxanthin could extremely significantly or significantly increase the levels of IL-2,IL-4,IL-6,TNF-α,IFN-γ,CD4,CD8,CD19,CD20 and the contents of immunoglobulin IgA,IgG and IgM in serum (P＜0.01 or P＜0.05),and extremely significantly increase the activities of SOD and CAT and the content of GSH in serum of immunosuppressed mice (P＜0.01).At the same time,astaxanthin could extremely significantly reduce the levels of ROS and MDA (P＜0.01).100 mg/kg astaxanthin had the best effect.【Conclusion】 100 mg/kg astaxanthin could improve the immune function and antioxidant capacity of immunosuppressed mice,effectively improve the immunosuppression caused by cyclophosphamide,and could be used to prevent immunosuppressed diseases and develop as a substitute feed additive for livestock and poultry.

Key words: Rhodotorula mucilaginosa; astaxanthin; mice; immunosuppressive; immune function