GC-Th cell–derived chemoattractants attract CXCR5⁺ T and B cells in a CXCL13-dependent manner. Conditioned media obtained from culture of GC-Th cells (shown as GC-Th) were used for chemotaxis assays. Fresh uncultured (medium) and conditioned media from GC-B cell cultures (B-CM) in the presence of SEB were used for negative controls. CXCL13 was added to upper chambers at 5 μg/mL. Anti-CXCL13 (or control antibody) was added at 25 μg/mL to lower chambers. The isotype control antibody did not inhibit the chemotaxis (not shown). After chemotaxis, the migrated cells were stained with fluorescent antibodies (anti–CD57-FITC, anti–IgD-PE, anti–CD4-PerCP, and anti–CD45RA-APC) to identify and numerate various tonsil lymphocyte subsets: CD4⁺CD45RA^–CD57^– memory T cells, CD4⁺CD57⁺ GC-Th cells, IgD⁺ naive B cells, and CD4⁺CD45RA⁺ naive T cells. The numbers of cells in the lower chambers (migrated cells) and in input cells were determined by FACS. Data are shown as percent migration of the indicated subsets. The error bars are the differences of duplicated experiments. Representative data from 3 independent experiments are shown.