Characterization of 6- to 8-week-old TxO mice. (A) TCL1 expression is shown by Western blot for WT, TCL1-tg, OCA-B^–/–, and TxO spleen cells. β-actin expression is shown in the bottom panel. (B) H&E staining of WT, TCL1-tg, OCA-B^–/–, and TxO spleens. Original magnification, ×40. Visualization was performed using an Olympus BX40 microscope with a UPlan 4×/0.13 NA air objective (Olympus America, Melville, NY). Images were collected with an Olympus DP10 camera and processed with Adobe Photoshop 7.0 (Adobe Systems, San Jose, CA). (C) Detection of B220⁺PNA^hi B cells by flow cytometry. Cells were untreated (top panels) or were stimulated with anti-IgM plus IL-4 (bottom panels).