| Two experiments were conducted to study on the effect of high selenium(Se) and low Se on the structure and function of immune system in chickens. The cell cycle and apoptosis of immune organs, the function of cellular, humoral and erythrocyte immunity, and the anti-oxidative function of spleen were determined by the means of pathology, immunology and flow cytometry.Experiment 1 Mechanisms of the immune functional changes caused by high Se in chickens300 one-day-old avian chickens were randomly divided into five groups, and fed on diets as follows: corn-bean control diet (Se 0.2mg/kg) and high Se diets (Se 1mg/kg, high Se group I ; Se 5mg/kg, high Se group II; Se 10mg/kg, high Se group III; Se 15mg/kg, high Se group IV) for 6 weeks. The results were as follow:①The volume, weight and relative weight of thymus, spleen and bursa of Fabricius(BF) were significantly decreased in high Se groups II , III and IV when compared with those of control group. Histopathologically, decreased lymphocytes, enlarged thymic corpuscle and increased nuclear debris in the center of corpuscles were appeared in the thymus. Decreased lymphocytes were observed in spleen and BF of high Se groups II, III and IV. Ultrastructurally, mitochondria injury and increased apoptotic cells with condensed nuclei were appeared in immune organs.②Cell cycle analysis by flow cytometry showed that the G0G1 phase was increased, and the S phase, G2M phase and proliferation index(PI) were decreased in thymus, spleen and BF of high Se II, III and IV. Changes of cell cycle were progressed with the dietary Se level increasing, and consistent with the changes of organs relative weight.③The percentage of Annexin-V positive cells measured by flow cytometry was higher in high Se groups II, III and IV than in control group. TUNEL assay showed that there were increased frequencies of apoptotic cells in high Se groups III and IV. Characteristic of ultrastructural features on apoptotic cells was nuclear membrane breakdown, chromatin condensation with horseshoe-like or crescent shapes. The results were consistent with suppressed growth and decreased lymphocytes of immune organs.④The percentage of CD3+ T cells, CD3+CD4+ T cells and CD3+CD8+ T cells were decreased variably in high Se groups II, III and IV groups when compared with those of control group. The mitogenic reponse of T lymphocytes to ConA and the contents of serum IL-2 were decreased in high Se groups III and IV than in control group. The results suggested that the cellular immune function of chickens was impaired by high Se.⑤The contents of serum IgG were lower in high Se groups III and IV than in control group. The contents of serum IgA and IgM were decreased in high Se group IV. Contents of serum total protein, albumin and globulin were decreased variably in high Se groups III and IV. The results suggested that humoral immune function of chickens was impaired by high Se.⑥The ratio of IC rosette was increased and the ratio of C3bR rosette decreased in High Se II, III and IV. Immune adherence function of erythrocyte was impaired by high Se.⑦The splenic Se and MDA contents were higher, and splenic GSH-Px, SOD and CAT activities, and total antioxidative ability were lower in high Se groups III and IV than in control group. The structure and function of spleen were impaired. The cellular and humoral function were decreased.Experiment 2 Mechanisms of the immune functional impairment caused by low Se in chickens120 one-day-old avian chickens were randomly divided into two groups. Corn, yellow bean and wheat, which were bought from Mianling count were used to formulated low Se diet (Se 0.0342 mg/kg). Sodium selenite was mixed into the low Se diet to produce 0.2 mg/kg Se diet (control group). Broilers were fed the diets for 6 weeks. The results were as follow:①The weight and relative weight of thymus, spleen and BF were significantly decreased in low Se group when compared with those of control group. Anatomically, the volume of immune organs were smaller in low Se group than in control group. Histopathologically, lymphocytes in thymus, spleen and BF were decreased. At 42 days of age, atrophy BF showed infolded epithelium, shrinked follicle with reticuloendothelial cells proliferation. Ultrastructurally, mitochondria injury and increased apoptotic cells with condensed nuclei were observed.②Cell cycle analysis by flow cytometry showed that the G0G1 phase was increased, and the G2M phase and proliferation index(PI) were decreased in thymus, spleen and BF of low Se group. Decreased proliferative function induced growth retardation of immune organs.③Increased apoptotic cells in thymus, spleen and BF were observed by the methods of flow cytometry, TUNEL stain and electron microscope. The results were associated with hypocellular of immune organs.④The percentage of CD3+ T cells and CD3+CD8+ T cells were decreased in low Se group. The mitogenic reponse of T lymphocytes to ConA and the content of serum IL-2 were lower in low Se group than in control group. The results showed that the cellular immune function of chickens was impaired by low Se.⑤The content of serum IgG, IgA, IgM, total protein, albumin and globulin were decreased iIn low Se group. The humoral immune function of chickens were decreased.⑥The ratio of C3bR rosette was decreased, and the ratio of IC rosette had no obvious change in low Se group. Primary lesion of erythrocyte's adherence function was induced by low Se.⑦The contents of splenic Se, total antioxidative ability, GSH-Px and CAT activities were decreased, and MDA contents in spleen increased in low Se group. The structure and function of spleen were impaired.The aforementioned results showed that the proliferative function of immune organs and activities of antioxidase in spleen were decreased, and the percentage of apoptotic cells of imunne organs and splenic MDA contents were increased by low Se (0.0342 mg/kg) and high Se (more than 5 mg/kg), which induced growth retardation of immune organs and decrease of cellular immune, humoral immune and erythrocyte's adherence function. The mechanisms of immune injury were closely related to the decreased cellular proliferative function, increased cellular apoptosis, decreased antioxidative ability and accumulated peroxidative products in the immune organs. In the present study, the effect of dietary Se on the structure and function of immune system was systematically researched for the first time. The results provided theoretical basis for determining reasonable supplemental dose of Se and preventing Se-deficiency and selenosis in chickens.
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