WASP and N-WASP are required for the B-cell immune response to TNP-KLH. WT, WKO, and cDKO mice were immunized by IP injection of TNP-KLH in alum and boosted 3 weeks later with another dose of TNP-KLH. Anti-TNP IgM (A) and anti-TNP IgG1 (B) Ab titers were determined by ELISA. Test samples were corrected for background binding. (C) Spleen sections from immunized mice at day 28 were labeled to detect GCs (peanut agglutinin positive) and MOMA⁺ metallophilic macrophages to define the MZ. GC areas were quantified and indicated in arbitrary units. Original magnification was 10×. (D) Quantification of GC B cells (B220⁺DAPI-GL7⁺Fas⁺) from immunized mice at day 28 by flow cytometry. Note the marked reduction of GC B cells in cDKO mice compared with WT mice. Each group represents 8 mice. Black bar represents the mean value for the group. *P < .05 compared with WT. (E) Schematic model of how WASP and N-WASP activity regulate peripheral B-cell homeostasis.