The Bu-1a+B lymphocytes in Fabricius bursa were cleared seriously,but it goes up significantly at the period of strong pathological changes in spleen and in blood .

• （4）法氏囊Bu-1a+B淋巴细胞的流失最为严重，脾脏和血液中B细胞在病变高峰期显著升高，对本病的免疫起着积极作用。