The bursae of Fabricius from the chicken and turkey were studied by light and electron
microscopy and immunohistochemical methods. The study focused on the relationship
of follicle-associated epithelium to the medulla. The follicle-associated epithelium
was supported by 3 to 5 layers of stratified epithelial cells which were a continuation
of the corticomedullary epithelial cells. The follicle-associated epithelium consisted
of M cells and scattered secretory dendritic cells. The network of the reticular epithelial
cells of the medulla was filled with secretory dendritic cells, B cells, and a few
T cells and macrophages. The cellular content of the follicle-associated epithelium
and the medulla suggested that they were different cellular compartments. Communication
between the follicle associated epithelium and medullary epithelial compartment occurred
through the supporting cells of the follicle-associated epithelium. When the supporting
layers of the follicle-associated epithelium infolded into the medulla, they formed
lamellated epithelial bodies similar to the thymic Hassall bodies. The lamellated
bodies enclosed secretory dendritic cells but not lymphocytes. The infolding of supporting
cells varied from follicle to follicle. The asynchronization of infolding contributed
to heterogeneity of follicle composition. Follicle heterogeneity was demonstrated
by differences in reactivity with a battery of monoclonal antibodies.
