The diffusely-infiltrated lymphoid tissue of the bursa of Fabricius of Sturnus unicolor. Histological organization and functional significance.

In the present study we confirm and extend previous reports about the existence of a T-dependent area in the bursa of Fabricius of some birds, analyzing ultrastructurally the cell content of the so-called diffusely-infiltrated lymphoid tissue of the bursa of the spotless starling, Sturnus unicolor. It consists of lymphocytes, plasma cells, macrophages (Mphis) and interdigitating cells (IDCs) in a supporting reticular stroma which, apart from blood capillaries, contains postcapillary high-endothelial venules (HEVs). The presence of both IDCs and HEVs confirms the T-cell-dependent nature of this area, as previously claimed for other avian species, and emphasizes other functions, apart from its role in B-cell maturation, for the bursa of Fabricius specially in adult birds.