Figure 2.

sjTREC are decreased in PBMCs with age. (a) Schematic diagram of T cell receptor excision circle (TREC) formation. TRECs are pieces of DNA fragments generated during TCR gene rearrangement in the thymus that are exported from the thymus to the periphery in T cell episomes. TRECs are not duplicated during mitosis and remain stable for a long time. However, as T cells divide, the level of TRECs is gradually diluted. Generation of TRECs occur in >70% of all new (naive) T cells, and they can be detected by PCR. (b) TREC levels in PBMCs from 160 healthy individuals at different ages (0 to 70 years old). (c) An inverse correlation between the TREC count and donor age was found.