Concurrent activation of NF-κB and Notch signaling induces splenomegaly and marginal zone expansion. (A) Heatmap of RNA-seq–based gene expression results (n = 2 biological replicates for each genotype) showing upregulation of NF-κB pathway genes Map3k14, Relb, and Nfkb2 in MZP B cells from NIK and TriB mice and upregulation of Notch signaling components Heyl, Myc, and Dtx1 in MZB cells from Notch mice and MZPs from TriB mice. Comparison with protein levels in Figure 3A. (B) FACS diagrams gated on B220⁺CD19⁺ B cells (left) or B220⁺GFP⁺ B cells (right) demonstrating a marked increase in MZPs (red rectangle) and MZBs (blue rectangle) in TriB relative to normal mice used as controls (Con; n = 10 in both groups). MZBs (CD21⁺CD23^−/dim) and MZPs (CD21⁺CD23⁺) are distinguished by level of CD23 expression. Table 1 provides additional data. (C) Photographic image depicting the difference in spleen size of age-matched 4-month-old Con and TriB mice. (D) Hematoxylin and eosin–stained tissue sections of spleens obtained from a 4-month-old Con mouse (left) and a TriB mouse (center and right). Original magnification, ×100 (left and center) and ×500 (right). Green, yellow, and red arrows denote small lymphocytes, scattered large transformed cells, and plasma cells, respectively.