Intact MZ B-cell migration in vivo and in vitro. (A) Intact B-cell chemotaxis toward CXCL13 in vivo: After LPS stimulation, CD19:KLF3 transgenic MZ B cells move into the B-cell follicle. Migration was induced by injecting 50 μg LPS (Fluka) in 200 μL of phosphate-buffered saline intraperitoneally.¹⁴  Mice were killed for analysis 3 hours later, and spleen cryosections were stained for Moma-1, IgM, and IgD. (A) Micrographs were obtained with an Apotome microscope, using a 10×/0.45 NA objective and the MosaiX Axiovision software module. (B) The proportion of MZ B cells migrating toward CXCL13 or S1P in vitro is the same for normal and KLF3 transgenic cells. Experiments were performed in duplicate or quadruplicate, respectively. Results were obtained from 2 independent experiments. Spontaneous migration was variable between experiments but always less than or equal to 10%. (C) Preestablished CD19:KLF3 MZ B cells are sessile and resistant to replacement by normal cells: B6 and B6.Ly-5.1 or CD19:KLF3 and B6.Ly-5.1 mice were parabiosed 3 weeks before analysis. The chimerism among the indicated lymphocyte subset was evaluated using FACS (CD4 T cells: CD3⁺ CD4⁺; CD8 T cells: CD3⁺ CD8⁺; follicular B cells: CD19⁺ CD21⁺ CD23⁺; MZ B cells: CD19⁺ CD21^hi CD23⁻). Graphs depict the chimerism among lymphocyte subsets in B6.Ly-5.1 mice (right panels) that were parabiosed with B6 mice (bottom left panel) or CD19:KLF3 mice (top left panel). Results derived from 2 independent experiments are shown (using 11 and 10 parabiotic couples, respectively).