Development of MCL in Eμ^CycD1CD19^CREBim^fl/flmice exposed to SRBC/irradiation or weekly SRBC. Spleens from mice treated with (A) SRBC and irradiation or (B) weekly SRBC show diffuse infiltration by cyclin D1–positive B cells (original magnification: ×20). Cyclin D1–positive B cells are shown invading (C) the liver of a mouse treated with weekly SRBC injections (original magnification: ×1000), (D) the lymph node (LN) of a mouse treated with SRBC and irradiation (original magnification: ×1000, ×40, ×40), and (E) the gastrointestinal (GI) tract of a mouse treated with SRBC and irradiation (original magnification, ×100).