| Themes > Science > Life Sciences > General Biology > Immunology > Recognition Systems in Immunity > The T cell Receptor for Antigen > Structure of the Thymus |
The thymus is an essential organ for the development of T cells. In mice (known as nude, since they also lack hair) and humans with diGeorge's syndrome the thymus fails to form fully and the result is a lack of T cells and a consequent severe immunodeficiency. The structure of this specialised organ for T cell development is a lobar one and reflects the hierarchical process of T cell development. Bone marrow precursors enter at the outer, sub-capsular region and migrate toward the centre of the lobe (medulla) through the cortex. The cortex is largely composed of a dense reticular network of a highly specialised thymic cortical epithelial cells, which appear to be the only cell type capable of mediating positive selection of thymocytes. In addition to the cortical epithelial cells a distinct type of medullary epithelial cell as well as bone marrow derived dendritic cells and macrophages are found in the thymus. The bone marrow derived cells appear to be the most efficient at triggering negative selection. Click here to see a diagram illustrating the structure of a thymic lobe |
|
|
