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Developmental Immunology
Volume 4, Issue 2, Pages 117-126

Kinetics of Thymocyte Subset Development and Selection Revealed by Cyclosporin A Treatment

1Imperial Cancer Research Fund, Human Tumour Immunology Group, The Courtauld Institute for Biochemistry, London W1P, 8BT, United Kingdom
2Department of Cellular Immunology, National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom

Received 23 May 1994; Accepted 24 October 1994

Copyright © 1995 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.


Cyclosporin A (CsA) inhibits the development of mature thymocytes from their CD4+ CD8+ precursors, but may allow autoreactive cells to mature. Using 3-color flow cytometry, we have followed the progressive development of thymocytes, including potentially autoreactive cells, during CsA treatment. Numbers of CD4+ CD8+ CD3high thymocytes dropped immediately, suggesting that the generation of these mature thymocyte precursors, normally dependent upon positive selection, was inhibited by CsA. Numbers of CD4- CD8+ thymocytes also declined rapidly, but CD4- CD8+ thymocytes were unaffected lfor 2 days, suggesting that the mature single-positive subsets are not symmetrically derived from a common GsA-sensitive precursor. An exceptional subset of CD8 SP thymocytes, expressing CD45RA, did not respond to CsA for about 10 days, indicating that they are distantly derived from a CsA-sensitive precursor. Apoptosis of TCR-Vβ3+ thymocytes caused by Mtυ-6, quantified according to the down-regulation of CD4 and CD8 on immature thymocytes, was partially inhibited by CsA, to maximal effect within 24 hours. This did not, however, facilitate their development into mature thymocytes.