Lymph node
Most T cells are, in time, eliminated in the thymus by a process of clonal deletion. However, some of them escape this process and are then "mopped up" in the lymph nodes. Lymph node stromal cells express peripheral tissue-restricted antigens (PTAs) on their surface. The Transcription factor "Aire" (autoimmune regulator) that controls the expression of PTAs on mTEC cells in the thymus is only expressed at low levels by uncharacterized double negative stromal cells. Most lymph node stromal cells preferentially express DF1, an Aire-like transcription modulator.