Conditional deletion reveals a cell-autonomous requirement of SLP-76 for thymocyte selection

The SH2 domain containing leukocyte phosphoprotein of 76 kD (SLP-76) is critical for pre-TCR-mediated maturation to the CD4(+) CD8(+) double positive (DP) stage in the thymus. The absolute block in SLP-76(null) mice at the CD4(-) CD8(-) CD44(-) CD25(-) (double-negative 3, DN3) stage has hindered our understanding of the role of this adaptor in alpha beta TCR-mediated signal transduction in primary thymocytes and peripheral T lymphocytes. To evaluate the requirements for SLP-76 in these events, we used a cre-loxP approach to generate mice that conditionally delete SLP-76 after the DN3 checkpoint. These mice develop DP thymocytes that express the alpha beta TCR on the surface, but lack SLP-76 at the genomic DNA and protein levels. The DP compartment has reduced cellularity in young mice and fails to undergo positive selection to CD4(+) or CD8(+) single positive (SP) cells in vivo or activation-induced cell death in vitro. A small number of CD4(+) SP thymocytes are generated, but these cells fail to flux calcium in response to an alpha beta TCR-generated signal. Peripheral T cells are reduced in number, lack SLP-76 protein, and have an abnormal surface phenotype. These studies show for the first time that SLP-76 is required for signal transduction through the mature alpha beta TCR in primary cells of the T lineage.