T-cell receptor excision circle (TREC)

T-cell receptor excision circles (TRECs) are small, circular pieces of DNA that are created during the development of T-cells in the thymus, an immune organ. They serve as markers indicating new T-cell production; because TRECs don't replicate when T-cells divide, their presence reflects recent T-cell formation. Measuring TRECs in blood helps assess the immune system’s ability to produce T-cells, which is important for diagnosing immune deficiencies like SCID. Essentially, TRECs provide a snapshot of how actively the thymus is generating new T-cells, crucial for a healthy immune response.