Studies On The Mechanisms Of Aflatoxin B₁-Induced Cellular Apoptosis Of Central Immune Organs In Broilers

Aflatoxin B₁, a toxic metabolite produced by some fungi, exerts hepatocarcinogenic and immunosuppressive effects. Previous studies have shown that excessive apoptosis of immune cells is a major factor in depressed immune function. One hundred and fifty-six one-day-old healthy Cobb broilers were purchased from Chia Tai Group ?Wenjiang, Sichuan, China?, and were randomly divided into two equal groups of three replicates and 26 birds per replicate, namely control group ?AFB₁<0.001 mg/kg? and AFB₁ group ?AFB₁=0.601 mg/kg?. This study was to investigate the mechanisms of aflatoxin B₁ induced apoptosis in broilers thymocytes and bursa of Fabricius ?BF? cells by the methods of histopathology, electron microscopy, TUNEL, flow cytometry and real-time quantitative PCR. The results were as follow.The relative weight of thymus was decreased. The amount of vacuoles and nuclear debris were increased in the cortex, and congestion in the medulla of thymus could be observed. Ultrastructural assessment showed that vacuolated mitochondria with degenerated cristae, and chromatin margination in lymphocytes can be easily found. The percentages of thymocytes with depolarized ??m and apoptosis rate of thymocytes were increased in the AFB₁ group. The mRNA expressions of Bax, Bak-1, cytC, Apaf-1, caspase-9, caspase-3, FasL, Fas and FADD were obviously increased ?p<0.01 or p<0.05?, while the mRNA contents of Bcl-2 and Bcl-xL were significantly decreased ?p<0.01 or p<0.05?. The contents of GSH and activities of SOD, CAT, GSH-Px and GR were decreased markedly ?p<0.01 or p<0.05?. The same trend was found in the mRNA expressions of SOD, CAT, GSH-Px and GR ?p<0.01 or p<0.05?. However, the content of MDA was increased in the thymus. The results showed that dietary AFBi could induce excessive apoptosis of thymocytes through mitochondrial and death receptor pathways.The relative weight of bursa of Fabricius was decreased. The decreased lymphocytes and increased nuclear debris were found in the folliculi lymphaticus. The ultrastructural assessment showed chromatin margination, enlarged mitochondria and endoplasmic reticulum in the lymphocytes and reticulocytes. The percentage of BF cells with depolarized ??m and apoptotic bursal cells were increased in the AFB₁ group. The mRNA expressions of Bax, Bak-1, cytC, Apaf-1, caspase-9, caspase-3, Grp78/Bip, Grp94 and CaM were up-regulated ?p<0.01 or p<0.05?, and relative mRNA expressions of Bcl-2 and Bcl-xL were decreased ?p<0.01 or p<0.05? in the BF cells in the AFB₁ group. The contents of GSH and activities of SOD, CAT, GSH-Px and GR were decreased markedly ?p<0.01 or p<0.05?. The same trend was found in the mRNA expressions of SOD, CAT, GSH-Px and GR ?p<0.01 or p<0.05?. However, the content of MDA was increased in the BF. The results showed that dietary AFB₁ could induce excessive apoptosis of BF cells through mitochondrial and endoplasmic reticulum pathways.In summary, dietary AFB₁ could increase the percentage of apoptotic thymocytes and BF cells. The mitochondrial pathways involved in the excessive apoptosis of thymocytes and BF cells. However, the death receptor pathoway and endoplasmic reticulum pathway involved in the apoptotic procedure of thymocytes and BF cells respectively. The oxidative stress may be an important mechanism related to the excessive apoptosis induced by dietary AFB₁.