The augmentation of antibody responses by preliminary intrabursal priming in the chicken.

Direct injection of antigen into bursal tissue of young chickens followed by subsequent intravenous immunization markedly stimulated agglutinin production against Brucella abortus. In contrast, preliminary intravenous immunization did not produce stimulation. The promoting effect of intrabursal injection was antigen-specific. Antigen injection into the bursa reduced the extent to which subsequent bursectomy suppresses the immune response. Bursa cells from young chickens which had been injected with antigen intrabursally were active in transferring the ability to give a secondary response to B. abortus when injected into bursectomized-irradiated chickens. The cells derived from chickens primed intravenously or from normal chickens were inactive. The implant of bursa cells from the 18-day-old chickens which had been injected with antigen intrabursally or intravenously at 11 days of age showed a promoting effect in restoring the ability to give secondary responses to both of B. abortus and Salmonella pullorum as compared with that of the implant of the bursa cells from unimmunized donors. These findings are discussed in relation to the existence of precursor cells that can respond to the antigen with a potential to enhance the antibody response to subsequent antigenic stimuli but are not yet mature enough to produce the antibody.