APOPTOSIS IN THE CHICKEN BURSA OF FABRICIUS INDUCED BY X-IRRADIATION

Immature B lymphocytes in the chicken bursa of Fabricius have previous ly been reported to undergo apoptosis by low doses of ionizing radiati on. In the present study, newly hatched chickens were subjected to who le-body X-irradiation, and the bursa of Fabricius was examined at vari ous postirradiation times by light and electron microscopy to obtain i nformation on the change of ultrastructure of irradiated bursal cells as well as on the time course and dose-response for the induction of a poptosis. Histological examination by light microscopy showed that pyk notic cells started to increase in the bursa within a few hours after irradiation and the frequency of occurrence reached a maximum at 6 hr. An evident increase of the pyknotic cells in number was observed at a dose of as little as 1 Gy, and the frequency increased with increases in the dose, reaching over 90% at 15 Gy. Electron microscopy of the i rradiated bursa revealed typical apoptotic morphology such as chromati n condensation, nuclear fragmentation, formation of apoptotic bodies a nd phagocytosis of pyknotic cells. Induction of apoptosis was also con firmed by the appearance of a typical DNA ladder pattern on agarose ge l. Thus, the present results demonstrate that the chicken bursal cells are hypersensitive to X-irradiation with regard to induction of apopt osis, and that the apoptotic bursal cells exhibit mosi of the ultrastr uctural features known to be typical of apoptosis.