Expression of the p56^lck Y505F Mutation in CD45-Deficient Mice Rescues Thymocyte Development

Abstract

Mice deficient in the transmembrane protein tyrosine phosphatase CD45 exhibit a block in thymocyte development. To determine whether the block in thymocyte development was due to the inability to dephosphorylate the inhibitory phosphorylation site (Y505) in p56^lck (Lck), we generated CD45-deficient mice that express transgenes for the Lck Y505F mutation and the DO11.10 T-cell antigen receptor (TCR). CD4 single-positive T cells developed and accumulated in the periphery. Treatment with antigen resulted in thymocyte apoptosis and the loss of transgenic-TCR-bearing cells. Peripheral CD45-deficient T cells from the mice expressing both transgenes responded to antigen by increasing CD69 expression, interleukin-2 production, and proliferation. These results indicate that thymocyte development requires the dephosphorylation of the inhibitory site in Lck by CD45.

ACKNOWLEDGMENTS

This research was supported by grants from the National Institutes of Health. J.R.S. is supported by the Division of Biology and Biomedical Sciences, Washington University. M.L.T. and K.M.M. are investigators of the Howard Hughes Medical Institute.

We thank our colleagues for comments and suggestions during the course of this research. We especially thank Paul Allen and Andy Chan for gifts of reagents and help with the ζ-chain and Y505 phosphorylation experiments, respectively.