Splenomegaly and plasma cell hyperplasia in old B^A20−/− mice. Cohort description: age range, 60 to 85 weeks; mean age of experimental group, 68 weeks; mean age of control group, 66 weeks. (A) Absolute cell numbers of splenocytes (n(B^A20−/−) = 10, n(control) = 9). (B) Left panel: Absolute cell numbers of B cells (CD19⁺; n(B^A20−/−) = 12, n(control) = 11). Right panel: Representative size and CD69 expression of splenic B220⁺ B cells. (C) Absolute cell numbers of splenic plasma cells (B220^loCD138^hi; n(B^A20−/−) = 10, n(control) = 9). (D) Representative immunofluorescence analysis of plasma cells in the spleen, plasma cells (red represents αCD138), B cells (green represents αB220). Bar represents 100 μm. (E) Titers of immunoglobulin isotypes in aged mice were determined by ELISA; n(B^A20−/−)= 12, n(control) = 11. (F-H) Absolute splenic cell numbers for the following cellular subsets: CD4 T cells. (F) Treg (CD4⁺CD25⁺); CD4⁺ naive (CD25⁻CD44^intCD62L^hi), memory-type (CD25⁻CD44^hiCD62L^hi), and effector T (CD4⁺CD44^hiCD62L^lo); CD8-T cells. (G) Naive (CD44^intCD62L^hi), memory-type (CD44^hiCD62L^hi), and effector T (CD44^hiCD62L^lo); myeloid cells (H): DC indicates dendritic cell (CD11c⁺); Eos, eosinophils (Gr1^intSiglecF⁺); Mac, macrophages (Mac1⁺Gr1^lo); and Neu, neutrophils (Gr1^hiLy6G⁺). n(B^A20−/−) = 5, n(control) = 5. (I) Serum IL-6 (pg/mL) in aged mice was measured by ELISA; n(B^A20−/−) = 12, n(control) = 11. (J) Representative stainings of IgG immune complexes in kidneys of B^A20−/− and control mice. Original magnification × 20. *P < .05 (1-way analysis of variance). **P < .001 (1-way analysis of variance).