PROGRAMMED CELL DEATH OF BURSAL LYMPHOCYTES INDUCED BY STEROID HORMONES

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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.