Impaired development of MZ and reduced lymph node and B1 B cells in TAK1-deficient mice. (A) Reduction of MZ B cells in the spleens of TAK1-deficient mice. Splenocytes from CD19CreTak1^+/+ and CD19CreTak1^fl/fl mice were stained with antibodies to B220, CD21, and CD23. Percentages indicate MZ B cells (CD21^hiCD23^lo) in the gated B220⁺ population. (B) Impaired MZ development in the spleens of TAK1-deficient mice. Frozen splenic sections derived from CD19CreTak1^+/+ and CD19CreTak1^fl/fl mice were stained with anti-MOMA-1 (green) and anti-IgM (red). The IgM⁺ MZ B-cell layers external to the ring of metallophilic macrophages are indicated with arrows. (C) Reduction of lymph node B cells in TAK1-deficient mice. Lymphocytes from the lymph nodes of CD19CreTak1^+/+ and CD19CreTak1^fl/fl mice were stained with anti-B220 and anti-Thy1.2 antibodies. The percentages of cells in the gated lymphoid populations are indicated. (D) Reduction of B1 B cells in the peritoneal cavities of TAK1-deficient mice. Cells from the peritoneal cavities of CD19CreTak1^+/+ and CD19CreTak1^fl/fl mice were stained with antibodies to IgM and CD5. The percentages of cells in the gated lymphoid populations are indicated. Data shown are representative of 9 (A), 3 (B,C), or 6 (D) independent experiments.