Lymphomas with a B1-like phenotype arise in the spleen and PerC of aged LMP1/CD30 mice. (A) Splenic weights and B- and T-cell numbers in the spleen of aged LMP1/CD30 mice compared with old control (ctrl) mice and young LMP1/CD30 mice. (B) Representative flow cytometric analyses of splenic B cells (CD19⁺) for CD43/CD23 and CD21/CD23 surface expression. Graph compiles the percentages of the CD21^lowCD23^low population of aged mice. (C) Flow cytometric analysis of splenic B cells to determine the percentage of PCs (B220^lowCD138⁺). Numbers represent means and standard deviations (SDs). (D) T cells in the spleen of aged mice were analyzed to determine the percentages and SDs of naïve T cells (CD62L^highCD44^low), central memory T cells (CD62L^highCD44^high), and effector memory T cells (CD62^lowCD44⁺). (E) Diagram showing total B-cell numbers in the PerC. (F) Flow cytometric analysis of the CD21^lowCD23^low population in blood B lymphocytes (CD19⁺). Numbers in the fluorescence-activated cell sorting plots indicate mean and SD values of the percentages of the gated populations. (G) Hematoxylin and eosin staining as well as anti-B220 (B cells) and anti-CD3 (T cells) immunohistochemistry of spleen sections of an aged ctrl and LMP1/CD30 mouse. Sections were scanned with an AxioScan.Z1 digital slide scanner (Zeiss, Jena, Germany) equipped with a 20× magnification objective (EC Plan-Neofluar 20×/0.50; Zeiss) and a Hitachi HV-F202SCL 3CCD camera. Imaging acquisition was performed using ZEN 2.3 SP1 blue edition imaging software (Zeiss) and NetScope Viewer Pro (Net-Base Software GmbH, Freiburg, Germany). (H) Kaplan-Meier curve of lymphoma development in LMP1/CD30 mice. Significance of lymphoma development was calculated by the log-rank (Mantel-Cox) test. *P < .05, **P < .01, ***P = .001, ****P < .0001.