PROGRAMMED CELL DEATH OF BURSAL LYMPHOCYTES INDUCED BY STEROID HORMONES

法氏囊是鸟类特有的淋巴器官，位于泄殖腔的背侧。当鸟受到处理、接种疫苗和高密度饲养等压力时，小鸡的法氏囊会减少。众所周知，应激期间肾上腺皮质分泌的糖皮质激素会导致法氏囊淋巴细胞的凋亡，从而导致法氏囊退缩。此外，当性成熟发生时，法氏囊会经历自发的退化。为探讨类固醇激素在法氏囊淋巴细胞凋亡中的作用，给四周龄公鸡一次性注射地塞米松1 mg/kg体重、苯甲酸雌二醇2 mg/kg、睾酮4 mg/kg或丙酸睾丸酮2 mg/kg，分别于1、2、4小时后处死。从法氏囊组织中提取DNA，在1.8%的琼脂糖凝胶中进行电泳，从地塞米松、苯甲酸雌二醇、睾酮和丙酸睾丸酮处理的鸡身上获得了“梯形图谱”，这是细胞凋亡的一个生化标志。根据这些结果，似乎有可能在鸡法氏囊自发退化的过程中，性类固醇可能诱导了细胞凋亡。在另一系列实验中，在注射地塞米松后2小时和48小时，免疫组织化学检测到泛素在法氏囊细胞凋亡中的表达，这一结果表明泛素可能参与了法氏囊细胞的凋亡。

The bursa of Fabricius is a lymphoid organ unique to avian species that is lacated dorsal to the cloaca. The chiken bursa decreases in sizu when the bird is subjected to stresses such as handling, vaccination and high-density rearing. Glucocorticoid secreted from the adrenal cortex during exposure to stress is known to cause apoptosis of bursal lymsphocytes, with resultant involution of the bursa. Furthermore, the bursa undergoes spontaneous regression when sexual maturation occurs. This study was undertaken in an attempt to clarify the role of steroid hormones in apoptosis of bursal lymphocytes by administering various steroids.Four-week-old male chickens were given a single injection of 1mg/kg body weight of dexamethasone, 2mg/kg of estradiol banzoate, 4mg/kg of testosterone or 2mg/kg of testosterone propionate and they were sacrificed 1,2 or 4 hr later. DNA was prepared from bursal tissue and subjected to electrophoresis in a 1.8% agarose gel.A "ladder pattern" on the electrophoretogram, which is a biochemical hallmark of apoptosis, was obtained from the following treated chickens : those treated with dexamethasone, estradiol benzoate, testosterone and testosterone propionate. It seems possible, from these results, that apoptosis might be induced by sex steroids during spontaneous regression of the chicken bursa. In another series of experiments, ubiquitin was detected immunohistochemically in apoptotic bursal lymphocytes 2 and 48 hr after an injection of dexamethasone, a result that suggests the possible involvement of ubiquitin in bursal apoptosis.