Impaired LPS-induced relocation of p100^−/− MZ B cells. (A) Wild-type or p100^−/− mice were injected with PBS or LPS as indicated. After 4 hours, spleens were removed and frozen sections were stained for IgM (blue) and MOMA-1 (brown). Note that a significant number of B cells remained outside the MOMA-1⁺ ring in spleens from LPS-treated p100^−/− mice. Images were acquired as in Figure 2E with a 20×/0.70 objective. (B) Impaired migration of p100^−/− MZ B cells to CXCL13. B-cell chemotaxis to CXCL13 and S1P was analyzed in Transwell assays. Error bars indicate SD from 3 to 4 experiments. Significant differences are indicated (Student t test, **P < .01; ***P < .002).