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Developmental Immunology
Volume 5 (1996), Issue 1, Pages 25-36

Thymic Medulla Epithelial Cells Acquire Specific Markers by Post-Mitotic Maturation

1INSERM U. 345, Institut Necker, 156 rue de Vaugirard, Paris Cedex 15 75730, France
2Institute for General and Experimental Pathology, University of Innsbruck, Innsbruck A-6020, Austria
3Department of Pathology and Immunology, Monash Medical School, Commercial Road, Prahran, Melbourne, Victoria, Australia

Received 17 October 1995; Accepted 9 January 1996

Copyright © 1996 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The development of thymocyte subsets and of the thymic epithelium in SCID and RAG-2-/– mice was monitored after normal bone-marrow-cell transfer. The kinetics of thymic reconstitution and their relationships with cell proliferation were investigated by using bromodeoxyuridine to detect DNA-synthesizing cells among lymphoid cells by 3-color flow cytometry, and in epithelial compartments by staining frozen sections. Thymocytes started to express CD8 and CD4 10 days after transfer, simultaneously with extensive proliferation. The first mature CD4+ single-positive cells were generated, from resting CD4+CD8+ cells after day 15. During this day 10–15 period, many epithelial cells positive for cortexspecific or panepithelial markers were labeled with BrdUrd after pulse-injection. Organized medullary epithelium also developed after day,15, that is, synchronously with the appearance of mature thymocytes, but medullary cells were never found BrdUrd+. These results suggest that, in these models, the reconstitution of the thymic epithelial network proceeds through expansion of preexisting cortical or undifferentiated cells and by later maturation (acquisition of specific markers) of medullary cells. This last process is dependent of the presence of mature thymocytes.