The Death Receptor Pathway Involved In The Protective Effects Of Sodium Selenite On The Excessive Thymocytes Apoptosis Induced By AFB₁ In Broilers

Aflatoxin B1(AFB1)is a potent immunosuppressive agent in endotherms,which could be related to the up-regulated of immune organs and the suppressive effect on the development of lymphocytes.This experiment was conducted to investigate the mechanism of death receptor pathway in the AFB1-induced thymocytes apoptosis.Two hundred and forty one-day-old Cobb broilers were divided into four groups,and chickens were fed an control diet(0 mg/kg AFB1),aflatoxin B1 containing diet(0.6 mg/kg AFB1),+Se group diet(0.4mg/kg Se as sodium selenite were supplemented in the control group diet)and AFB1+Se group diet(0.4mg/kg Se as sodium selenite were supplemented in the AFB1 group diet)for 3 weeks.For investing the mechanisms of the death receptor pathway involved in the protective effects of sodium selenite on the excessive thymocytes apoptosis induced by AFB1 in broilers,the relative weight of thymus,T-cell subsets,percentage of apoptotic cells and relative expression of apoptosis regulatory genes in thymus were observed at 7,14 and 21 days of age.Results were as follow:Compared with the control group diet,AFB1 diet could decrease the relative weight of thymus.Histopathologically,the major lesions of the thymus were a lot of debrits in the cortex in the AFB1 group.It was observed that the percentages of thymic CD3+,CD3+CD4+ and CD3+CD8+ T-cell subsets were decreased.However,the ratio of the CD4+/CD8+ was increased.Expectedly,excessive apoptosis of thymocytes was observed in the AFB1 group,also the relative mRNA expressions of RIP,caspase-8,caspase-9,caspase-3,Fas,FasL,ASK1,IKIP and JNK were up-regulated and those of Bcl-2,NF-kBl and Bid were down-regulated through the qRT-PCR analysis.Compared with control group,there were no significant change of the relative weight,pathological changes and percentages of apoptosis in the thymus in the +Se group and AFB1+Se group,also the decreased percentages of thymic CD3+,CD3+CD4+ and CD3+CD8+T-cell subsets and the increased ratio of the CD4+/CD8+were observed in those groups.Meanwhile,the increased relative mRNA expression of Fas?TNF-??Caspase-8?JNK and ASK1,the decreased relative mRNA expression of NF-kB1 were observed.The sodium selenite supplementation diet,compared with the AFB1 group,could increase the relative thymus weight,alleviate histological lesions,reduce the incidence of apoptotic thymocytes,decrease the relative mRNA expression of JNK,TNF-a,caspase-8,caspase-3 and caspase-9 and increase the relative mRNA expression of Bid and Bcl-2,however the changes of relative mRNA expression of Fas,NF-kBland IKK were not observed.Conclusion:It was speculated the mechanisms of the AFB1-induced excessive apoptosis of thymocytes could be related to the following three death receptor pathways:? AFB1 could induce directly the apoptosis of thymocytes through the Fas-FasL-FADD-caspase8-caspase3 pathway;? Fas could take part in the excessive apoptosis through Fas-Daxx-ASK1-JNK-Bcl-2 pathway in the mediate of mitochondria;? The constitutive activation of the TNF-a-RIP1-IK IP-NF-kBl-caspase-3 could be a novel pathway contributed to the apoptosis of thymocytes induced by AFB1.The selenium supplied into the dietary containing 0.6 mg/kg AFB1 could alleviate the lesions in thymus,and decrease the percentages of apoptotic cells through blocking the above mentioned death receptor pathway ? and ?.