Immune capacity of the chicken bursectomized at 60 hr of incubation: cytoplasmic immunoglobulins and histological findings.

Chickens were surgically bursectomized at 60 hr of incubation, before the bursal anlage appears. Completeness of the bursectomy was confirmed at autopsy at 10 weeks of age. These embryonically bursectomized (Bx)3 chickens are known to produce immunoglobulins of IgM, IgG, and IgA classes but so far no specific antibodies have been observed even after heavy immunization. The Bx chickens had mature plasma cells in an almost normal frequency when studied at 10 weeks of age. The amount of germinal center formation in the spleen and cecal tonsils was markedly decreased when compared to the control (Co) chickens. Also, the frequency of cytoplasmic IgA-positive (c-IgA+) cells was severely decreased in the Bx animals, whereas the occurrence of c-IgG+ and c-IgM+ cells was not affected to the same extent. These findings support the hypothesis that heavy-chain class switch may occur without the bursal influence, and that the bursa of Fabricius is essential only for expansion or creation of the antibody repertoire.