Cells,Tissue,and Organs of the Immune System Lymphoid System Bone Marrow Organs of the immune system are shown.Primary organs are represented by upper case repre sented in red. Primary Lymphoid Organ Tymus amd bursa of Fabricius The thymus serves as a central lymphoid organ to control maturation of T cells which function in cell-mediated immunity.The bursa of Fabricius,in birds,is responsible for the antigen-in-dependent maturation of B cells involved in the humoral immunity. The bursa of Fabricius is a lymphoepithelial organ seen as an intestinal pouch in birds,but not in mammals.If the bursa Fabricius is removed,the birds will have normal cell-mediated immunity,but will not produce antibodies in response to an Cells, Tissue, and Organs of the Immune System Organs of the immune system are shown. Primary organs are represented by upper case letter and are label in black. Secondary organs of the immune system are represented by lower case and are in red. Several lymph nodes are also lower case and are labeled in red. Primary Lymphoid Organ Tymus amd bursa of Fabricius The thymus serves as a central lymphoid organ to control maturation of T cells which function in cell-mediated immunity. The bursa of Fabricius, in birds, is responsible for the antigen-in-dependent maturation of B cells involved in the humoral immunity. The bursa of Fabricius is a lymphoepithelial organ seen as an intestinal pouch in birds, but not in mammals. If the bursa Fabricius is removed, the birds will have normal cell-mediated immunity, but will not produce antibodies in response to an