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This study aimed to evaluate the comparative effects of aflatoxin-contaminated corn on the thymus and bursa of Fabricius (BF) in chickens by detecting histopathological lesions, cell cycle phase distribution and apoptosis. A total of 900 COBB500 male broilers were randomly allocated into five groups. The experiment lasted for six weeks and the five dietary treatments consisted of uncontaminated corn (control), 25% contaminated corn, 50% contaminated corn, 75% contaminated corn and 100% contaminated corn groups. The gross changes showed the decreased size of the thymus and BF, as well as the pale color of the BF in the broilers after aflatoxin contaminated diet exposure. There were more nuclear debris in the thymus and BF of birds in the 50%, 75%, and 100% contaminated corn groups, but the pathological impairments of the BF were more obvious than those of the thymus, which showed as more obvious lymphocyte depletion and the proliferation of reticulocytes and fibroblasts. At 21 days of age, the percentage of thymocytes and BF cells in the G2M phase was increased in a dose-dependent manner in the four AFB-contaminated corn groups. However, at 42 days of age, dietary AFB1 induced cell cycle perturbation at the G0G1 phase in thymocytes, but at the G2M phase in BF cells. The increased percentage of apoptotic cells in the thymus and BF were similarly observed in the AFB groups. According to these results, the severity of histopathological lesions may be correlated with the different sensitivity of the two central immune organs when exposed to AFB; different arrested cell cycle phases suggest that different mechanisms may be involved in the lesions of the thymus and BF, which need to be further researched.

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Cell-mediated cytotoxic responses are critical for control of Marek's disease virus (MDV) infection and tumour development. However, the mechanisms of virus clearance mediated by cytotoxic responses in the bursa of Fabricius of chickens during MDV infection are not fully understood. In this study, the host cytotoxic responses during MDV infection in the bursa were investigated by examining the expression of genes in the cell lysis pathways. Partial up-regulation existed in the expression of the important cytolytic molecule granzyme A (GzmA), Fas, NK lysin and DNA repair enzyme Ape1, whereas little or no expression appeared in other cytolytic molecules, including perforin (PFN) and Fas ligand (FasL), and molecules involved in DNA repair and apoptosis in the bursa during MDV infection. These results suggest that less sustained cytotoxic activities are generated in the bursa of MDV-infected chickens. The findings of this study provide a more detailed insight into the host cytotoxic responses to MDV infection.

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The dynamics of the serum concentration of protein 27 (P27) of avian leukosis virus and transforming growth factor beta2 (TGF-beta2) were compared during the period between 29 and 59 weeks of age in two flocks of broiler chicken breeding stock undergoing outbreaks of severe lymphoid leukosis (LL) associated with persistent high mortality (susceptible) and in another two flocks of breeding stock with the presence of avian leukosis virus in association with low mortality due to LL (resistant). The average mean concentration of serum P27 in the LL-susceptible flocks was significantly higher (p<0.05) than that in the LL-resistant flocks in six out of seven samplings performed at 5-week intervals, between 29 and 59 weeks of age. The peak in the average rise of serum P27 in the LL-resistant flocks (309 pg/ml) was associated with the highest level of TGF-beta2 (1282 pg/ml) among all flocks and at all sampling times. The significance of TGF-beta2 in inhibition of lymphoid tumour development is discussed.

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The ability of the bursa of Fabricius to regenerate after gamma-irradiation and bone marrow reconstitution was examined in chickens thymectomized (TX) immediately after hatching. Irradiation (2 X 500 R) 3 weeks after hatching was followed by impaired bursa regeneration, as judged both by bursa/body weight ratios and by bursa follicle development 3-6 weeks later in TX as compared to control birds. Germinal center formation in the spleen was deficient, and immune responses to sheep erythrocytes (SRBC) and B. abortus (BA) were moderately reduced in the TX as compared to control birds irradiated at 3 weeks but not in TX birds irradiated at 5 weeks of age.

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Individual immature chickens were socially stressed when placed into an established group of chickens. The stress response was determined by periodic measurement of plasma cortisol and by determination of the relative regression of the bursa of Fabricius. Stressed chickens had elevated cortisol levels during the first 24 hours following the initiation of social stress. The bursa-to-body-weight ratios of stressed birds at 96 hours following stress were significantly lower than the ratios in control birds, and their tuberculin reaction was significantly depressed. Newcastle disease virus was more invasive and attained higher titers in stressed birds. The hemagglutination-inhibition (HI) response of the stressed birds was higher in one trial and lower in another.

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The response of intact and bursectomized chicks to stressful stimuli has been examined. The stressors imposed were: a. fast-acting ACTH adminstration; b. immersion in cold water; c. starvation. In Bursa-intact chicks the results were as follows: 1. Plasma corticosterone was increased by all stimuli. 2. Adrenal corticosterone was decreased by ACTH treatment while it was increased by immersion in cold water and by starvation. 3. Plasma glucose was increased by ACTH administration and cold water immersion and decreased by starvation of the birds. 4. Adrenal ascorbic acid concentration was not influenced by all stimuli. 5. Adrenal weights were found to be increased by ACTH and starvation treatments only. 6. Bursa weights were increased by ACTH administration. 7. A very low concentration of corticosterone was found in the Bursa of Fabricius. Bursectomized chicks differed from the intact ones in the following: 1. Plasma and adrenal corticosterone concentrations were not increased by starvation. 2. Plasma glucose increased moderately with ACTH administration. 3. Adrenal ascorbic acid was depleted by all stimuli but was not related to the corticosterone level in the adrenals and blood plasma.

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