Immunoglobulins, Antibodies and the Bursa of Fabricius: Induction of Agammaglobulinemia and the Loss of All Antibody-Forming Capacity by Hormonal Bursectomy

Hormonally bursectomized (HBx) chickens were repeatedly immunized with Brucella antigen. The proportion of antibody-responding HBx chickens increased from 16% at 6-day primary, to 48% at 6-day secondary, and to 60% at 15- and 21 day-tertiary. Despite this continued immunization, however, 40% of the HBx chickens still remained completely unable to produce any detectable antibody response even with the use of an extremely sensitive agglutinin assay. Following a secondary immunization with HGG 64% of HBx chickens failed to produce any detectable antibody. Natural hemagglutinins to rabbit red blood cells were also absent from the sera of HBx chickens. Serum immunoglobulins were determined by immunodiffusion and immuno-electrophoresis using specific anti IgM and IgG sera. Serum IgG levels were quantitated with the use of an extremely sensitive assay employing the inhibition of precipitation of 125I-labeled IgG by specific antiserum. Approximately 50% of HBx chickens had less than 1% of the control IgG level. Some birds were completely agammaglobulinemic, having less than 1/10,000 the control amount of IgG. Several of the HBx chickens with about 1% of IgG had normal or elevated levels of IgM. Serum α2-macroglobulin levels were normal in HBx chickens. Several HBx chickens that survived until 8 months of life were rechallenged with various antigens. A total lack of antibody production to most antigens was still found, even though some of these birds had considerable amounts of IgG and/or IgM. In vitro cultures of spleen and appendix confirmed the serum results on immunoglobulins, in showing that lack of circulating IgG and IgM was associated with a failure of its synthesis. The results presented in this paper strongly deny claims that bursectomy cannot totally prevent the development of all antibody-forming capacity or immunoglobulin synthesis. They reinforce the concept of an absolute dissociation of immunologic responsiveness in chickens, in that the bursa is the sole site of control of the development of the antibody-forming system.