Peripheral blood (PB) and spleen leukemic burden is decreased in the p50^−/−;TCL1 mice. (A) Immunoblots were performed in mouse spleen cell lysate from p50^+/+, p50^+/−, and p50^−/− mice (all TCL1⁺). Spleen lysate from a TCL1-transgenic animal and lysate from the Mec1 cell line were used as a positive controls for TCL1 and p50, respectively. Actin is shown as a loading control. The line on the blots indicates where additional control lanes have been removed. (B) PB was monitored for the presence of CD19⁺/CD5⁺ leukemic cells starting at 4 months. Leukemia is defined as >10% CD19⁺/CD5⁺ cells. (C) Spleens were isolated from mice at time of sacrifice based on meeting early removal criteria. A representative image of spleens from littermate p50^+/+;TCL1 and p50^−/−;TCL1 animals is shown. (D) Hematoxylin-and-eosin (H&E) histology was performed on sections of spleens isolated from 4- to 7-month-old p50^+/+;TCL1 and p50^−/−;TCL1 animals (N = 6 per genotype). Representative images from each genotype at original magnification ×10 and ×60 are shown.