 Through the action of AIRE, medullary thymic epithelial cells (mTEC) express major proteins from elsewhere in the body (so called "tissue-restricted antigens" - TRA) and T cells that respond to those proteins are eliminated through cell death (apoptosis).Thus "AIRE" drives negative selection of self-recognizing T cells.When AIRE is defective, T cells that recognize antigens normally produced by the body can exit the thymus and enter circulation.