THE IMMUNOLOGICAL ROLE OF DIFFERENT LYMPHOID ORGANS IN THE CHICKEN

SUMMARY The development of lymphoid tissue in the bursa of Fabricius in the chicken has been prevented by the injection in ovo of testosterone propionate. A small proportion of the hatched chickens were also shown to have a complete atrophy of the thymic cortex. The immunological responses of these hormonally‐treated chickens have been studied using several types of antigenic challenge. In birds deprived of all bursal lymphoid tissue, but still possessing a normal thymus, no circulating antibody was detected after challenge with five classical antigens. Delayed hypersensitivity reactions to tuberculin or vaccinia virus were nearly completely inhibited. However, the rejection time of random skin homografts, and the production of lesions on the CAM by the blood cells of these birds were completely normal. In birds showing a complete atrophy of the thymic cortex as well as of bursal lymphoid tissue, the rejection of skin homografts was also prevented, although the production of CAM lesions by blood cells was still normal. It was concluded that in the chicken there are two and possibly three primary levels of lympbocytopoiesis, each controlling populations of cells concerned with different types of immunological response.