| Popis: |
Vertebrates have evolved a lymphocyte based adaptive immune system which specifically recognises antigens (Pancer and Cooper, 2006). The lymphoid progenitor cells migrate to the thymus a primary lymphoid organ for the development of T cells (Yang et al., 2010; Zlotoff and Bhandoola, 2011). Progenitor cells undergo a stringent selection process which leads to the development of T cells which have a T cell receptor that specifically reacts with the foreign antigens and not with the self antigens. The pre-T cells further differentiate into many subpopulations in the thymus or the peripheral organs, which perform different functions and are responsible for the adaptive immune responses. The maturation and development of T cells is typically defined by the expression of specific cell surface receptors. The early immature thymocytes that do not express either CD4 or CD8 are called double negative (DN) thymocytes. At these stage the cells undergo the rearrangement of T cell receptor (TCR) く chain. Subsequently, these cells express both CD4+ CD8+ and are referred to as the double positive (DP) cells. During this stage, the rearrangement of the α chain of TCR happens and the cells express the complete T cell receptor (Kreslavsky et al., 2010). The DP thymocytes undergo proliferation and depending on the strength of TCR signaling further develop into either CD4+ or CD8+ single positive (SP) T cells via repression of the gene encoding the other receptor. |
