**5. Maturation and selection of T cells**

Maturation is the condition of developing progenitor within the thymus parenchyma, where the cells known as thymocytes, undergoes various developmental processes to perform exclusively. These cells can be recognized based on manifestation of various markers on the cell surface and the antigen presenting cells present the T cells with self and foreign antigen [11]. It usually consists of positive selection in which the lymphocytes that recognize the foreign antigens survived and reached to the maturity then enter the medulla through the cortex. Later, goes to the other sites in the body via blood [9]. Maturation is a very complicated process and only a small number of lymphocytes reach to the stage of maturity in the thymus. The negative selection in which the lymphocytes which are incapable to distinguish the self-antigens are eliminated by the macrophages. This is approximately 95% of the total cells.
