Infiltration of the spleen by malignant lymphocytes in TCL1 and Par-4 × TCL1 mice. Tissues were collected from mice that met euthanasia criteria and analyzed for infiltration by leukemic B cells. (A) Formalin-fixed paraffin-embedded spleen sections stained with hematoxylin and eosin viewed at original magnification ×10 and ×60 showing infiltration of neoplastic round cells. (B) Mass of spleens excised from animals upon euthanasia, with representative images from the indicated genotypes. (C) Spleens and bone marrow from euthanized animals were analyzed via flow cytometry for infiltration by CD45⁺CD5⁺CD19⁺ leukemia cells. Bars indicate the mean, with error bars representing the standard error of the mean. (D) Representative dot plots of spleen and bone marrow flow from euthanized TCL1 and Par-4 × TCL1 mice.