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Developmental Immunology
Volume 3 (1994), Issue 4, Pages 265-271

Positive Selection by Purified MHC Class II / Thymic Epithelial Cells In Vitro: Costimulatory Signals Mediated by B7 Are Not Involved

1Department of Anatomy, The Medical School, University of Birmingham, Birmingham B15 2TT, UK
2Department of Biological Sciences, Keele University, Keele, Staffordshire, ST5 5BG, UK

Received 21 July 1993; Accepted 23 September 1993

Copyright © 1994 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.


We have investigated the possibility that the costimulatory signals required for activation of mature T cells also play a role in providing differentiation signals for positive selection during T-cell development. We show that purified MHC Class II+ thymic epithelial cells are able to support positive selection in vitro but lack both the functional capacity to deliver costimulatory signals and expression of the costimulatory ligand B7. Our results suggest that the additional signals provided by costimulatory ligands are not required for TCR-mediated positive selection, although other ancillary signals provided by thymic epithelial cells may be involved.