Notch1 activation supported via Dll1 from Cd4⁺T cells. (A) Graphic representing the identification of Notch1 signaling as a central component of all data presented in Figures 1 to 5. (B) Messenger RNA quantification of Notch receptors and (C) representative blot and relative protein quantification of activated Notch1 in Eµ-TCL1 and Eµ-TCL1^Akt-C mice at 3 to 4 months and 7 to 8 months via flow cytometry, respectively. (D) Representative blot of activated Notch1 in Cd5^– and Cd5⁺ B cells via flow cytometry in Eµ-TCL1 and Eµ-TCL1^Akt-C mice at 7 to 8 months. (E) Representative blot and relative protein quantification of Dll1 in B cells, T cells, and macrophages in Eµ-TCL1 and Eµ-TCL1^Akt-C mice at 3 to 4 months and 7 to 8 months via flow cytometry. (F) Dll1 phycoerythrin (PE) on splenic T cells at 3 to 4 months and 7 to 8 months. (G) Dll1 PE on splenic Cd4⁺ T cells at 3 to 4 months and 7 to 8 months. (H) Representative blot of Dll1 on splenic Cd4⁺ and Cd8⁺ T cells in Eµ-TCL1 and Eµ-TCL1^Akt-C mice at 7 to 8 months. (I) Percentage of Cd8⁺ T cells from Cd19-Cre, Eµ-TCL1, and Eµ-TCL1^Akt-C mice. Respective quantification of Cd4⁺ Foxp3^– T cells (J) and of Cd4⁺ Foxp3⁺ regulatory T cells (K). *P < .05, **P ≤ 0.01, ***P ≤ .001 (unpaired, 2-sided Student t test).