Junctional sequences of T cell receptor γδ genes: Implications for γδ T cell lineages and for a novel intermediate of V-(D)-J joining

Abstract Nucleotide sequences of a large number of V-(D)-J junctions of T cell receptor (TCR) γ and δ genes show that most fetal thymocytes express on their surface one of just two γδ TCRs known to be expressed by epidermal γδ T cells (s-IEL) or intraepithelial γδ T cells associated with female reproductive organs (r-IEL). In contrast, γδ TCRs expressed on adult thymocytes are highly diverse as a result of multiple combinations of gene segments as well as junctional deletions and insertions, indicating that developmental time- and cell lineage-dependent mechanisms exist that control the extent of γδ TCR diversity. In addition, this study revealed a new type of junctional insertion (P nucleotides), which led to a new model of V-(D)-J joining generally applicable to immunoglobulin and TCR genes.