Pediatric Department B, Edmond and Lily Safra Children's Hospital, Sheba Medical Center, Tel Hashomer, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
Curr Opin Allergy Clin Immunol. 2011 Dec;11(6):517-24. doi: 10.1097/ACI.0b013e32834c233a.
The thymus gland provides an environment for the production of rearranged diversified populations of T-cell receptors (TCRs) expressed on peripheral T cells. These receptors respond to nonself-antigens and are tolerant to self-antigens. During TCR rearrangement processes, unused excised DNA fragments create byproducts termed TCR excision circles (TRECs). Although these byproducts have no function, their detection in the peripheral blood stream is a clear indication that a rearrangement process has occurred. Their enumeration in the latest circle created during TCR delta deletion and the final TCR alpha rearrangement can determine thymus output.
Since the first description of its monitoring changes in the frequency of recent thymic emigrants with age and in human immunodeficiency virus (HIV)1 infection, TREC assessments have been used in many clinical settings in which T-cell immunity is involved, including diagnosing, understanding and monitoring T-cell immunodeficiencies, HIV infection, aging, autoimmune diseases and immune reconstitution after bone marrow transplantation.
Confounding factors, such as cell division, cell death, longevity of the naïve T cells, and intracellular degradation, are known to affect TREC levels, yet measurement of TREC content is still considered the most reliable tool for tracking recent thymic emigrants. Its recent implantation for neonatal screening to diagnose severe combined immunodeficiency by using dry blood spots from Guthrie papers makes TREC the most accurate noninvasive tool to detect T-cell immune disorders. Together with determination of the TCR repertoire, TREC contents can give a clear insight into peripheral T-cell homeostasis.
胸腺为外周 T 细胞表达的重组多样化 T 细胞受体（TCR）的产生提供了一个环境。这些受体对外来抗原作出反应，对自身抗原具有耐受性。在 TCR 重排过程中，未使用的切除 DNA 片段产生称为 TCR 切除环（TREC）的副产物。尽管这些副产物没有功能，但在外周血流中检测到它们清楚地表明发生了重排过程。在 TCR δ 删除和最终 TCR α 重排过程中最新创建的环中对其进行计数可以确定胸腺输出。
自首次描述其监测年龄和人类免疫缺陷病毒（HIV）1 感染时近期胸腺迁出细胞频率的变化以来，TREC 评估已在许多涉及 T 细胞免疫的临床环境中使用，包括诊断、理解和监测 T 细胞免疫缺陷、HIV 感染、衰老、自身免疫性疾病和骨髓移植后的免疫重建。
细胞分裂、细胞死亡、幼稚 T 细胞的寿命和细胞内降解等已知的混杂因素会影响 TREC 水平，但 TREC 含量的测量仍被认为是跟踪近期胸腺迁出细胞的最可靠工具。最近，它被用于通过 Guthrie 滤纸的干血斑进行新生儿筛查以诊断严重联合免疫缺陷，这使得 TREC 成为检测 T 细胞免疫紊乱的最准确的非侵入性工具。与 TCR 库的测定相结合，TREC 含量可以清楚地了解外周 T 细胞的稳态。
