Bursa of Fabricius
Follicle of the bursa of Fabricius of a chicken (HE) (1)
The follicles of the bursa of Fabricius consist of a three dimensional meshwork of reticulo-epithelial cells of which the intercellular spaces are filled with (B) lymphocytes, lymphoblasts and macrophages.
The cortex contains mesenchymal reticular cells, macrophages and more closely packed, small B lymphocytes, what causes the darker color.
The medulla contains a more heterogeneous cell population but the total number of cells is lower , hence the paler color. The medulla contains mostly lymphoblasts, medium to small B lymphocytes, macrophages, secretory dendritic cells and reticular epithelial cells.