Differential requirement of Thymic Epithelium for ab and gd T cell development

초록

It is well known that the mainstream T cells interact with microenvironment during development in the thymus. In contrast, it was not clear if γδ T cells also require specific thymic microenvironment or not. In order to study the thymic epithelial cell (TEC) subsets during T-cell development, a transgenic system, enabling inducible cell-specific ablation as well as marking the TEC subsets using bicistronic bacterial nitroreductase and EGFP genes, was established. Transgenic mice expressing EGFP in their TECs by 3.1kb and 9.1kb TSCOT promoter, named 3.1T-NE and 9.1T-NE respectively, were generated. In adult life, EGFP was expressed in the medulla with a 3.1 kb TSCOT promoter, whereas it was in the cortex with a 9.1 kb promoter, suggesting putative TEC specific as well as compartment specific cis elements within two promoters. Nitroreductase induced cell death was specific without bystander killing upon the treatment of prodrugs such as nitrofurantoin and metronidazol dose dependently. The fetal thymic organ cultures (FTOCs) that analyzed based on the expression levels of EpCAM, MHCII, CDR1 and/or UEA-1. The EGFP expression patterns varied among subsets indicating the differential TSCOT promoter activity in each TEC subset. Prodrug treatment in FTOCs reduced the numbers of total and subsets of thymocytes. A CD4+CD8+ double positive cell population was highly susceptible in both transgenic lines. There was a distinct reduction in γδ T cell population only in the 9.1T-NE thymus, indicating that they require a NTR-EGFP expressing TEC population. Therefore, these results support a division of labor within TEC subsets for the αβ and γδ lineage specification.