Development of the peripheral immune function in the chicken

The bursa of Fabricius was surgically separated from the rest of the gut‐associated lymphoid tissue (GALT). The antigens, sheep red blood cells (SRBC) and killedBrucella abortusorganisms, were introduced into the bursal lumen, into the gut only, or allowed to get in contact with both (controls). The antibody titres in serum, the development of the bursal weight and the bursal histology were studied at various ages. The control birds responded vigorously to both antigens at between 2 and 8 weeks of age. At that age, the isolated bursa was capable of producing full anti‐Brucellaresponse, but not the anti‐SRBC response, suggesting that SRBC need collaboration between both bursal and intestinal T and B cells. After 8 weeks, the cells in the gut alone were as potent as those in the gut and the bursa together at producing antibodies to SRBC. The bursal weight was significantly higher in theper bursamimmunized chickens, indicating that continuous presence of antigens in the bursa may postpone its involution.