Abstract
After a tightly regulated developmental program in the thymus, “mature” single positive (SP) thymocytes leave the thymus and enter the periphery. These newly arrived recent thymic emigrants (RTEs) are phenotypically and functionally immature, and will complete a dynamic maturation in the peripheral lymphoid organs before being licensed to be resident naïve T cells. To study the early events occurring in the RTE maturation process, we identified the phenotype of CD4+ pre-RTEs, a population of CD4+ SP thymocytes that have acquired the thymus egress capability. Compared to peripheral naïve T cells, CD4+ pre-RTEs displayed superior survival capability in lymphoreplete mice and faster proliferation under lymphopenic condition. The differences in Bcl2/Bim expression and/or heightened IL-7 signaling pathway may account for the pre-RTEs’ better responsiveness to homeostatic signals. Qa2, the expression of which indicates the phenotypic maturation of SPs and RTEs, was found to be upregulated in CD4+ pre-RTEs in thymic perivascular space. Migratory dendritic cells that surround this region contribute to Qa2 expression in pre-RTEs. The dendritic cell-driven Qa2 induction of CD4+ pre-RTEs is independent of MHC class II and Aire molecules.
Highlights
Recent thymic emigrants (RTEs) comprise the population of peripheral T cells that have recently completed a tightly regulated developmental program in the thymus and entered the circulating naıve pool
Boursalian et al have shown that GFPhi T cells in the periphery are RTEs that have left the thymus within a week [17]
We focused on the ones in adult animals (SP4 thymocytes) and investigated their phenotypic and homeostatic properties
Summary
Recent thymic emigrants (RTEs) comprise the population of peripheral T cells that have recently completed a tightly regulated developmental program in the thymus and entered the circulating naıve pool. RTEs are phenotypically and functionally distinct from resident naıve T cells in the periphery [17,18,19,20,21,22,23,24,25]. Secondary lymphoid organs (SLOs) and DCs are important for the maturation process of RTEs in the periphery over a 2–3-week period [17,26,27]. Despite of these findings, very little is known about the molecular mechanism of this maturation process
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