The bursa of Fabricius: the evolution of a discovery.

It has been a joy these past 40 yr to have traveled the "Bursal Road"--a road we helped construct and whose route allowed us to make a variety of observations that contributed either to basic science or indirectly or directly to the role of the bursa of Fabricius in the B cell repertoire. The chicken's bursa of Fabricius introduced me to endocrine, heritability, and growth studies, which allowed serendipity to occur and the revelation of the classical and modification of the classical theses of bursal function. The modification of the classical thesis, presence of immunoglobulin in the absence of the bursa, raised questions that directed us to study hypothalamic control of behavior, which was not directly related to bursal function. This forced us to learn various techniques, e.g., autoradiography, cell labeling, and electron microscopy, that made it possible to study long- and short-lived lymphocytes, lymphokines, labeled cells, and the fine structure and function of the bursa of Fabricius, cecal tonsil, Harderian gland, lymph nodes, Meckel's diverticulum, Pineal gland, and spleen. In an attempt to use cyclophosphamide to understand how the spleen acquired the ability to produce antibodies, we revealed a dendritic cell in the bursa, the bursal-secretory dendritic cell (BSDC), and in the spleen, the ellipsoid-associated cell (EAC). The BSDC is a novel cell in the bursal microenvironment and may be involved in an interaction with prebursal or bursal stem cells, leading to the differentiation or selection of the B cell repertoire of the chicken.