*2.3.3 Agonist selection takes place in the thymic medulla*

The agonist selection is also undertaken by the thymic medulla to allow a portion of autoreactive CD4+ T cells to differentiate into regulatory T (Treg) cells that express forkhead box P3 (Foxp3). These regulatory T cells that are derived from the thymus are referred to as tTreg cells and move from the thymus to the peripheral tissues. They constitute the majority of all Treg cells and play the central role in immune tolerance. So, the thymus must be precisely effective in the generation of Treg cells. If this could not be achieved, then we see the process of autoimmunity. However, there are Treg cells derived from peripheral tissues referred to as pTreg cells. This type of Treg cells is especially accumulated at sites of inflammation and consequently regulates inflammatory responses [6].
