REGULAR ARTICLES

Cell Research (2003); 13(4):265-273

Kinetics of thymocyte developmental process in fetal and neonatal mice

Shi Yun XIAO^*, Yan LI^*, Wei Feng CHEN^**

Department of Immunology, School of Basic Medical Sciences, Peking University Health Science Center, 38 Xueyuan Road, Beijing 100083, China

Received Feb-26-2003 Revised April-28-2003 Accepted May-2-2003

Correspondence: Prof. Wei Feng CHEN Department of Immunology, School of Basic Medical Sciences, Peking University Health Science Center, 38 Xueyuan Road, Beijing 100083, China. 0086-10-62092593 (phone) 0086-10-62091436 (fax) wfchen@public.bta.net.cn *The first two authors contributed equally to this study.

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Kinetics of thymocyte development in vivo during embryogenesis was pursued. The early development of thymocytes in the fetal and neonatal BALB/c mice was discontinuous, with four waves of cell proliferation occurring at fetal day (Fd) 14 to 17, Fd 18 to day (D) 1 after birth, D 2 to D 5 and D6 thereafter. The first three proliferation waves coincided with the generation of CD4^hiCD8^hi (DP), TCR⁺CD4^hiCD8^-/lo (CD4 SP), and TCR⁺CD4^-/loCD8^int/hi (CD8 SP) thymocytes, respectively. The transition from DN to DP cells was further investigated and it was found out that there were two differential pathways via immature single positive (ISP) cells in the BALB/c mice, each functioning at different fetal ages. One is via TCR^-CD4^-CD8⁺ cells, occurring between Fd 15 and Fd 17 and the other is via TCR^-CD4⁺CD8^- cells, occurring from Fd 17 until birth. In contrast, the TCR^-CD4^-CD8⁺ pathway dominated overwhelmingly in the C57BL/6 mice. These findings shed new light on the hypothesis that the differential pathway preference varies with mouse strains. With respect to the shift in the intensity of CD4 and CD8 expression on thymocytes from fetal to adult mice, the TCR⁺CD4^hiCD8^-/lo, and TCR⁺CD4^-/loCD8^int/hi subsets might be equivalent to the medullary type TCR⁺CD4/CD8 SP cells.

Key words: fetal thymus, neonatal mice, thymocyte ontogeny.