Abstract: Apoptosis and dynamic expression of their regulatory genes Bcl-2 and Bax in lymphocytes of bursa of 21-day -old SPF chickens infected with SNJ93 strain from the first to fourteenth day post infection were investigated. Apoptosis was observed by electron microscope and apoptosis rate was assessed by TUNEL method. The expression of Bcl-2, Bax was investigated by immunohistochemical ABC method. The apoptosis of lymphocytes in bursa of chickens infected with SNJ93 strain from the first to seventh day post infection significantly increased compared with that of normal SPF chickens (P<0.01).The expression of BCL-2 significantly increased in lymphocytes of bursa of SPF chickens infected with SNJ93 strain from the first to nineth day post infection compared with those of normal chickens (P<0.01). The expression of Bax significantly increased from the first to seventh day post infection (P<0.01 or P<0.05).The ratio of bcl-2 and Bax significantly decreased from the first to fifth day post infection (P<0.05 or P<0.01). A great deal of disappearance of lymphocytes of bursa of SPF chickens infected with SNJ93 strain from the first to seventh day was related to apoptosis .The ratio of Bcl-2 and Bax could precisely reflect the degree of apoptosis of lymphocytes of bursa.

Key words: SPF chickens, Bursa of Fabricius, Bpoptosis, Bcl-2, Bax