DYRK1a is essential for peripheral B-cell maintenance and B-cell–mediated autoimmunity. (A) Flow cytometric analyses of B220⁺ B cells and T-cell receptor (TCR) β⁺ T cells in the spleen (SP), inguinal lymph nodes (iLN), and Peyer’s patches (PP) of WT or Dyrk1a^BKO mice (6-8 weeks old). (B-D) Flow cytometric analyses of immature (Imm; B220⁺CD93⁺) and mature (B220⁺CD93⁻) B cells (B), T1 (CD93⁺IgM⁺CD23^–) and T2 (CD93⁺IgM⁺CD23⁺) immature B cells (C), and follicular (FO, B220⁺CD21^intCD23⁺) and marginal zone (MZ; B220⁺CD21^hiCD23⁻) B cells (D) in the spleen of WT and Dyrk1a^BKO mice (6-8 weeks old). (E) A representative spleen image (left) and a summary graph of spleen weight (right, each circle represents a mouse) of WT and Dyrk1a^BKO mice that were either not treated (NT) or injected with CD4 T cells from BM12 mice for 3 weeks. (F-G) Flow cytometric analysis of B220⁺ B cells (F) and B220⁻CD138⁺ plasma cells (G) in WT and Dyrk1a^BKO mice that were injected with BM12 CD4 T cells for 3 weeks. Data are presented as a representative plot (left) and summary graph (right) based on multiple recipient mice. (H) ELISA of autoantibodies reacting against double-stranded DNA (anti-dsDNA) and nuclear antigen (ANA) in serum from WT and Dyrk1a^BKO mice injected with BM12 CD4 T cells for the indicated time periods. (I) Confocal microscopic analyses of glomerular IgG and C3 deposition in kidney sections from WT and Dyrk1a^BKO mice injected with BM12 CD4 T cells for 3 weeks. Scale bar, 1 mm. The arrows depict colocalization of IgG and C3. Data are representative of 3 independent experiments. Summary graphs are presented as mean ± SD, and P values were determined by an unpaired, 2-tailed Student t test (A-B,H). *P < .05; **P < .01; ***P < .001.