Conditional knockout of A20 in B cells induces severe defects in B-cell development and differentiation. (A) A20 protein expression in CD43-depleted B cells after 4-hour culture with or without 10 μg/mL LPS. (B-E) Absolute cell numbers were calculated from 5 to 7 age-matched mice per genotype. Data are mean ± SD. (B) Absolute splenocyte and B-cell numbers of the indicated genotypes. (C) Absolute cell numbers of splenic mature (B220⁺AA4.1⁻), marginal zone/marginal zone precursor (MZ; MZ-P: B220⁺CD1d^highCD21^high), follicular (B220⁺AA4.1⁻CD1d⁻CD23⁺), and transitional (B220⁺AA4.1⁺) B cells. (D) Representative proportions of transitional (Trans: B220⁺AA4.1⁺) and mature (B220⁺AA4.1⁻) B cells of total lymphocytes (top panels) and of follicular (FO: CD1d^intCD21^int) and marginal zone/marginal zone precursor (MZ: CD1d^highCD21^high) B cells of CD19⁺ B cells (bottom panels) in the spleen. (E) CD23 expression on B220⁺CD1d^hiCD21^hi B cells (left panel). Absolute cell numbers of marginal zone (B220⁺CD1d^hiCD21^hiCD23^lo) and marginal zone precursor (B220⁺CD1d^hiCD21^hiCD23^hi) B cells (right panel). (F) Top panels: Immunofluorescence of spleen sections: green represents αB220, B cells; red, αCD3, T cells; and blue, laminin. Bottom panels: Immunohistochemistry of spleen sections: blue represents MOMA-1, metallophilic macrophages; and brown, CD1d-expressing cells. Bar represents 100 μm. (G) Proportions of B220^loCD138^hi plasma blasts in splenic B cells 3 days after LPS treatment. (H) Blimp1 mRNA expression relative to porphobilinogen deaminase was determined by real-time PCR in splenic B cells 3 days after LPS treatment. (I) Antigen-specific IgM and IgG3 serum titers in response to T-independent immunizations with 10 μg NP-Ficoll determined by ELISA. Lines represent geometric means for 5 mice per experimental group. *P < .05 (1-way analysis of variance). **P < .001 (1-way analysis of variance).