Panel a illustrates the process of TREC and KREC assays. On the right side, it shows the generation of signal joint TRECs (sjTRECs) in the thymus during T cell differentiation between the Immature Single Positive (ISP) and Double Positive (DP) stages. This process involves the excision of the Delta locus between the recombination excision circle (REC) and the J segments, occurring in around 80 percent of T cells. sjTRECs are small episomal circular DNA fragments that are not replicated during subsequent T cell division and are directly proportional to thymic T cell production. On the left side, it shows the generation of signal joint KRECs (sjKRECs) in the bone marrow during B cell differentiation between the Small preB and immature B stages. This process involves the excision of the C segment between the intron recombination signal sequence (RSS) and the de elements, occurring in around 30 percent of positive cells and 100 percent of positive cells (around 50 percent of all B cells). Like sjTRECs, sjKRECs are not replicated and are directly proportional to B cell production. Coding joint (cj)KRECs are on the genomic DNA and are proportional to the total number of B cells. The log2(cjKREC/sjKREC) corresponds to the mean number of B cell divisions since the K inactivation. Panel b shows two plots summarizing the samples and types of analysis included in the study according to children's age. The horizontal axis represents children's age in weeks. The vertical axis represents individual children. Different shapes and colors indicate the type of analysis performed (TREC olink_MS, TREC olink, TREC) and the group (Preterm, Term). The plot shows the distribution of samples across different ages and analysis types, with preterm and term groups distinguished by different symbols.
Cohort design and TREC analysis description. (a) Scheme of TREC and KREC assay. Right: sjTREC are generated in the thymus during T cell differentiation, between the ISP and DP stages. It corresponds to the excision of the delta locus excision between the δREC and the ΨJα segments. This rearrangement occurs in around 80% of αβ T cells. sjTRECs are small episomal circular DNA without an origin of replication, so they are not replicated during subsequent T cell division and are directly proportional to thymic T cell production. Left: KREC are generated in the bone marrow during B cell differentiation, between Small preB and immature B stages. It corresponds to the invalidation of the nonfunctional κ chain, by excision of the Cκ segment between the intron recombination signal sequences (RSS) and the κde elements. This rearrangement occurs in around 30% of κ+ cells and in 100% of λ+ cells (around 50% of all B cells). Like sjTREC, sjKREC are not replicated and are directly proportional to B cell production. CjKREC are on the genomic DNA and are so proportional to the total number of B cells; log2(CjKREC/sjKREC) corresponds to the mean number of B cell division since the K invalidation. HSC, hematopoietic stem cell; TSP, thymic seeding progenitor; DN, double negative; ISP, immature single positive; DP, double positive; SP, single positive. (b) Summary of samples and type of analysis included in the study according to the children’s age. N represents number of samples according to analysis performed and the shape of the point to the preterm or term group.