T lymphocyte development in p⁵⁶^lck deficient mice: allelic exclusion of the TcR β locus is incomplete but thymocyte development is not restored by TcR β or TcR αβ transgenes

Abstract

The protein tyrosine kinase, p56lck, is involved in signal transduction in mature T cells and in the molecular events controlling early thymocyte differentiation. Thymuses of mice deficient for p56lck expression (p56lck‐/‐) consist of immature CD4‐CD8‐ double‐negative (DN) and CD4+CD8+ double‐positive (DP) thymocytes and are severely reduced in total cell number. In this report we have studied DN thymocytes from p56lck‐/‐ mice and found an increase in the proportion of the CD44−CD25+ subset, suggesting that transit through this stage, which is known to require T cell receptor (TcR) β expression, may be delayed in the absence of p56lck expression. In addition, the expression of a transgenic TcR β chain or TcR αβ pair did not restore thymic development in p56lck‐/‐ mice. However, in contrast to mice expressing a dominant negative isoform of p56lck in which DP thymocytes do not develop, DP thymocytes still develop in nontransgenic and TcR transgenic p56lck‐/‐ mice. These results demonstrate that expansion of the DP subset is impaired in p56lck‐/‐ mice. In contrast, allelic exclusion is not severely compromised. Although there was an increase in the number of peripheral T cells expressing more than one Vβ chain in TcR transgenic p56lck‐/‐ mice, we found that inhibition of endogenous TcR β gene rearrangement was almost complete in thymocytes of Vβ transgenic p56lck‐/‐ mice and we could not detect any peripheral T cells that expressed more than one Vβ chain in non‐transgenic p56lck‐/‐ mice. Copyright © 1995 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim