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 bird s, analyzing ultrastructurally the cell content of the so-called diffu sely-infiltrated lymphoid tissue of the bursa of the spotless starling , Sturnus unicolor. It consists of lymphocytes, plasma cells, macropha ges (Mos) and interdigitating cells (IDCs) in a supporting reticular s troma which, apart from blood capillaries, contains postcapillary high -endothelial venules (HEVs). The presence of both IDCs and HEVs confir ms the T-cell-dependent nature of this area, as previously claimed for other avian species, and emphasizes other functions, apart from its r ole in B-cell maturation, for the bursa of Fabricius specially in adul t birds.