Effects of BF-sensitization on immune responses at different stages of development in chicks

Effects of administration of two antigens, sheep red blood cell (SRBC) and Brucell abortus (BA), via the bursa of Fabricius (BF-sensitization with antigens) on immune responses were studied in growing chicks. The effects of BF-sensitization with a bacterial antigen (BA) on IgA-producing cell count in the lamina propria of the jejunum were also examined. Antibody liters were significantly increased by BF-sensitization from 1 weeks of age to 11 weeks of age. Maximal augmentations of anti-SRBC and -BA antibody productions were observed in chicks BF-sensitized at 6 to 8 weeks of age. Responses after 4 and 7 days of intravenous booster injection of SRBC in chicks received the BF-sensitization at 1 and 6 weeks of age were higher than those of control chicks which received the i.v. administration alone. The responses were also higher than the control in chicks received the BF-administration of BA at 1, 6 and 11 weeks. Augmentation of antibody productions after the i.v. booster injection were maximal in chicks received the administration via the BF at 6 weeks of age, except for the response at 4 days after the i.v. injection of BA. Number of anti-SRBC-antibody-producing cells were increased by BF-sensitization from 1 week of age to 15 weeks of age, with maximal augmentation in chicks sensitized at 6 weeks of age. The counts after booster i.v. injection were also increased in chicks BF-sensitized from 1 week of age to 15 weeks of age. The counts received the i.v. booster injection were also maximal in chicks BF-sensitized at 6 weeks of age. Numbers of IgA-producing cells in the lamina propria of the jejunum were significantly increased by BF-sensitization with BA at 9 weeks of age as compared with those of age-matched untreated chicks. These results suggested that follicle-associated epithelium (FAE) of the BF contributed to establishment of the intestinal defence mechanism by IgA-producing lymphocytes as estimated in M cells of ruminants