Effect Of AFB₁on Immune Organs In Broilers

180one-day-old avian male broilers were randomly divided into four equal groups. The control group was fed on corn-soybean basic diet, and AFB1group I, AFB1group II and AFB1group III were fed on diets containing0.15,0.3and0.6mg/kg AFB1, respectively. The samples were taken at7,14and21days of age. The experiment was conducted with the objective of examining the impact of AFB1on immune organs in broilers by histopathology, flow cytometry (FCM), biochemistry and ELIS A method.Results were showed as follows:Compared with control group, the feed conversion ratio (FCR) was increased and the immune organ index was decreased in AFB1group Ⅱ and AFB1group III. By histopathological observation, the lesions were observed in AFBi group II and AFB1group Ⅲ. In thymus, the congestion in medulla, unclear nuclei of many reticular cells in cortex and many nuclear debris around the nucleus were oberved. In bursa of Fabricius, the number of lymphocytes in medulla of the follicle was decreased, there were many vacuoles in cortex and medulla of the follicle, and the number of nuclear debris in the vacuole was increased. In spleen, the congestion in red pulp and vacuoles in lymphatic nodule and periarterial lymphatic sheath were observed, and the number of nuclear debris in the vacuole was increased. Ultrastructural changes of immune organs were observed in AFB1group III. The dilated perinuclear cisternae and vacuolated mitochondrial were observed in thymocyte, and increased apoptotic lymphocytes were often around reticular cells or phagocytized by reticular cells. In bursa of Fabricius, the number of apoptotic lymphocytes was increased, and some apoptotic cells were phagocytized by reticular cells. In spleen, dilated perinuclear cisternae and swollen mitochondrial were observed in splenocyte, and the number of apoptotic lymphocytes was increased. By biochemistry method, it was indicated, in spleen, the content of non-enzymatic antioxidants (GSH) and the activities of antioxidants (GSH-Px, GR and CAT) were decreased and the content of lipid peroxidative product (MDA) was increased in AFB1group Ⅱ and AFB1group Ⅲ. As measured by flow cytometry and TUNEL assay, the percentages of apoptosis cells in thymus, bursa of Fabricius and spleen were increased and the percentages of CD3+, CD3+CD4+and CD3+CD8+T cells in spleen and peripheral blood were decreased in AFB1group II and AFB1group III. The expressions of Bax and Caspase-3were increased in thymus, while the expression of Bcl-2was decreased. The expression of Caspase-3was increased in bursa of Fabricius in AFB1group II and AFB1group III, but the expressions of Bax, Bcl-2and Caspase-3were little in spleen. By ELISA method, it was showed that the contents of IL-2, IFN-y, IgG, IgA and IgM in serum were decreased in AFB1group II and AFB1group III.It was concluded that dietary AFB1concentration at the level of0.3and0.6mg/kg could cause pathological lesions in immune organs, reduce the antioxidative capacity in spleen and increase lipid peroxide which may induce oxidative damage. The percentage of apoptosis cells were increased in immune organs when the dietary AFB1concentration at the level of0.3and0.6mg/kg, the mechanism on increased apoptosis was associated with the expression of apoptosis protein. The regulatory mechanism of apoptosis was different among three immune organs. The percentage of mature T cells in spleen and peripheral blood and the contents of IL-2and IFN-y in serum were decreased, which may result from the lesion of thymus. The contents of IgG, IgA and IgM in serum were decreased, which may result from the lesion of bursa of Fabricius and spleen.