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Department of Immunology, Peking University Health Science Center, Beijing, China
Our previous studies have defined a differentiation program followed by the newly generated single-positive (SP) thymocytes before their emigration to the periphery. In the present study, we further characterize the development of CD4SP cells in the thymic medulla using mainly intrathymic adoptive transfer assays. By analyzing the differentiation kinetics of the donor cells, which were shown to home correctly to the medullary region following adoptive transfer, we established the precursor–progeny relationship among the four subsets of CD4SP thymocytes (SP1–SP4) and demonstrated that the progression from SP1 to SP4 was unidirectional and largely synchronized. Notably, while the phenotypic maturation from SP1 to SP4 was achieved in 2–3 days, a small fraction of donor cells could be retained in the thymus for a longer period, during which they further matured in function. BrdU incorporation indicated that cell expansion occurred at multiple stages except SP1. Nevertheless, CFSE labeling revealed that only a limited number of cells actually divided during their stay in the medulla. As to the thymic emigration, there was a clear bias toward cells with increasing maturity, but no distinction was found between dividing and nondividing thymocytes. Collectively, these data not only provide solid evidence for a highly ordered differentiation program for CD4SP thymocytes, but they also illustrate several important features associated with the developmental process.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work was supported by grants from National Natural Sciences Foundation (30330520 and 30525044) and Natural Basic Research Program of China (2006CB504300 and 2006CB910101).
2 Address correspondence and reprint requests to Dr. Wei-Feng Chen and Dr. Yu Zhang, Department of Immunology, Peking University Health Science Center, 38 Xue Yuan Road, Beijing, 100083, China. E-mail addresses: wfchen{at}bjmu.edu.cn and zhangyu007{at}bjmu.edu.cn
3 Abbreviations used in this paper: DP, double-positive cells; NKT, natural killer T cell; PI, propidium iodide; RTE, recent thymic emigrants; S1P1, sphingosine 1-phosphate receptor-1; SP, single-positive cells; Treg, regulatory T cell.
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  M. A. Weinreich and K. A. Hogquist Thymic Emigration: When and How T Cells Leave Home J. Immunol., August 15, 2008; 181(4): 2265 - 2270. [Abstract] [Full Text] [PDF]
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