MZ B cells and MZMs are reduced, and S aureus uptake aberrant in WASP-deficient mice. Immunohistochemistry of spleen sections from WT and WASP^−/− mice. (A) Schematic representation of a B-cell follicle and the MZ in the spleen. Black arrows indicate the MZ. (B) Reduced number of MZ B cells (CD1d⁺ B220⁺) and normal localization of metallophilic macrophages (MOMA-1⁺ Sialoadhesin⁺) in WASP^−/− spleens relative to WT spleens. Black arrowhead represents the MZ. (C) Normal localization of red pulp macrophages (F4/80⁺), CD11b⁺ macrophages, and DCs (CD11c⁺). (D) Reduced number of MZMs (MARCO⁺ SIGN-R1⁺) in WASP^−/− spleens compared with WT spleens. Black arrow represents MZMs in the MZ. (E) Localization of S aureus 30 minutes after intravenous injection. Note that S aureus almost exclusively colocalize with MARCO⁺ MZ macrophages in WT mice, whereas WASP^−/− mice show aberrant localization of S aureus. White arrowhead represents the MZ. FO indicates B-cell follicle; MZ, marginal zone; RP, red pulp. Original magnifications: panels B to D, ×10; D, ×20.