Abstract: Objective The apoptosis and expression of Caspase-3,Bcl-2 proteins in lymphocytes throughout the post embryonic development of the Tian Fu meet duck bursa of fabricius were studied in order to explore the mechanism of B-lymphocytes apoptosis. Methods The Tian Fu meet ducks from 0-29 weeks posthatching period were divided into 11 groups, 5 ducks per group.The routine HE, terminal deoxynucleotidyl transferase mediated dUTP-biotin nick endlabeling(TUNEL)，and immunohistochemical methods were used. Results From 0-3 weeks posthatching period, the apoptosis index of lymphocytes in the medullar of follicle rose, whereas that in the cortex of follicle remained the same. The apoptosis indexes of lymphocytes in the medullar and cortex of follicle decreased at the 5th week and maintained at this level until the 14th week, and then increased at the 17th week, reaching their plateaus at the 29th week. During 0-14 weeks, the apoptosis indexes of lymphocytes in the medullar of follicle in each group was higher than that in the cortex, and lower than that in cortex from 17-29 weeks. The changing pattern of Caspase-3 expression in lymphocytes was paralleled positively with that of apoptosis index, while that of Bcl-2 expression in lymphocytes was reversely with that of apoptosis index (except 5-14 weeks). Conclusion The lymphocyte apoptosis exists universally in the duck bursa during the post embryonic development period which undergoes obvious age-related changes. The expression patterns of Caspase-3 and Bcl-2 proteins in lymphocytes might be one of the crucial mechanisms in such age-related changes of lymphocytes apoptosis.

Key words: Post embryonic development of bursa of fabricius, Bc1-2 protein, Caspase-3 protein, TUNEL, Immunohistochemistry, Tian Fu meet duck