Morphological and histochemical characterization of the medullary cells in the bursal follicles of the chicken.

Using light and electron-microscopy and enzyme-histochemical methods the cells in the follicular medulla of the chicken bursa of Fabricius were characterized. The following cell types were identified: lymphocytes of both B and T cell series, lymphoblasts, plasma cells, dendritic reticulum cells and histiocytic reticulum cells--the latter being the only cells phagocytosing the tracer substance used (colloidal carbon). The medullary cells observed showed electron-microscope and histochemical characteristics typical of the germinal center cells in mammalian lymphoreticular tissues. Furthermore, a distinct bursal follicular epithelial cell was identified, and so was a medullary epithelial structure resembling Hassall's corpuscle of the thymus. These findings give further support to the idea that the avian bursa has functions of a peripheral lymphoid organ as well as containing T-derived lymphocytes.