WASP-deficient mice show reduced specific immune response to TNP-Ficoll. WT and WASP^−/− mice when 12 to 14 weeks old were injected intravenously with 2.5 μg of TNP-Ficoll. (A) Uptake of TNP-Ficoll in spleens 30 minutes and 3 hours after injection. (Left panel) Spleen sections were labeled to detect TNP-Ficoll and MOMA⁺ metallophilic macrophages to define the MZ. Note the reduced TNP staining in the MZ at 30 minutes (top panels) and in the follicles at 3 hours (bottom panels) in WASP^−/− mice compared with WT mice (original magnification ×20). (Right panels) MZ B cells were labeled with anti-TNP and analyzed by flow cytometry (n = 5). (B) Anti-TNP IgM and IgG3 antibody titers were determined at day 7 after immunization by enzyme-linked immunosorbent assay. Each group represents mean values (± SD) from n = 5 mice, which were corrected for background binding. FO indicates B-cell follicle; MZ, marginal zone; non-B, lymphocytes negative for CD21 and IgM; RP, red pulp. *P < .05, **P < .01.