A reliable and simplified sj/β-TREC ratio quantification method for human thymic output measurement

Current techniques to peripherally assess thymic function are: the signal-joint T-cell receptor excision circle (sj-TREC) level measurement and the naive T cell and CD31+ TREC-rich subset determination. However, all of them are indirect approaches and none could be considered a direct recent thymic emigrant (RTE) marker. To overcome their limitations, Dion et al. (2004) described the sj/β-TREC ratio that allows the peripheral quantification of the double negative to double positive intrathymic proliferation step. Nevertheless, the protocol described is expensive, sample and time-consuming, thus, limiting its usefulness. In this study, we describe a simplified protocol that reduces from 33 to 9 the amount of PCR reaction needed but maintaining the sensitivity and reproducibility of the original technique. In addition, we corroborated the effectiveness of our technique as an accurate thymic output-related marker by correlating the peripheral sj/β-TREC ratio with a direct measurement of thymic function as the percentage of double positive thymocytes (r = 0.601, p < 0.001).