MTS/ΔSLP CD4⁺ T cells do not initially possess an activated-like phenotype. (A) Diagram of constructs that permit selective induction of the MTS mutation via tamoxifen treatment. (B) Western blot analysis of total SLP-76 protein in purified T cells isolated from mice of various genotypes (left) and expression of YFP protein in CD4⁺ T cells 2 days after tamoxifen treatment. Populations are gated on CD4⁺ T cells. ΔSLP denotes a floxed WT allele of SLP-76, which was deleted after tamoxifen treatment. (C) Surface expression of activation markers using flow cytometry of +/ΔSLP (solid line) and MTS/ΔSLP (shaded) mice 2 days after tamoxifen treatment. Histograms are gated on YFP⁺CD4⁺ T cells. Data are representative of 5 independent experiments using 2 or 3 mice per group. (D) Intracellular staining for the incorporation of BrdU in +/ΔSLP and MTS/ΔSLP mice. Histograms are gated on YFP⁺CD4⁺ T cells. Data are representative of 2 independent experiments using 2 mice per group.