Critical Role Of Space Telorism In Education Of Thymocytes By Thymus

Background and Purpose: The thymus is the primary organ for thymocytes maturation and development. Immature T cell precursors derived from bone marrow migrate to the thymus and accumulate under the thymus capsule, and move inward through the cortex and cortico-medullary junction toward the thymic medullary. In the thymus, the thymocytes undergo series complex process, including proliferation, receptor gene rearrangement, positive selection by MHC, negative selection for eliminating the self-reactive and defective cells, the maturation of the surface molecular and the function of the cells, and finally migrate via the circulation to the secondary lymphoid organs. It is assurance that the peripheral mature T cells can recognize the exogenic antigens and self MHC complex (the self MHC restriction) and eliminate the self-reactive T cells (self tolerance). Every step during this process proceeds the microenvironment of the thymus which contains thymic stromal cells and extrecellular matrix. It is well known that thymic stromal cells are the most important part that form the three-dimensional mesh structure in thymus. Interaction between the thymocytes and the stromal cells in thymus different compartments insure completing the positive and negative selection accurately and orderly, as well as promoting the development and maturation of T cells by participation of thymin and cytokines secreted by thymic stromal cells. In a word, the thymic stromal cells provide the most suitable microenvironment for educating the thymocytes either in time or in space, which is the determinative factors during the thymocytes differentiation, and forming the functional subset.The thymus is well known to play key roles not only in establishing and shaping a functional T cell repertoire, but also in inducing and maintaining self-tolerance as well as deletional transplantation tolerance. It has been widely studied that the stable immune tolerance induction is mainly rely on the thymus selection mechanisms, i.e., positive and negative selection. Recently, it has been found that the thymic stromal cells widely express...