CXCL13/CXCR5 signaling promotes membrane ruffling and LFA-1–supported contacts to enhance antigen gathering at the B-cell IS. (A) Time-lapse DIC, IRM, and fluorescence antigen images (in gray scale and color-coded scale) of representative MD4 B cells on membranes with tethered HEL (20 molecules/μm²) alone or with CXCL13. White arrows indicate monitored antigen gathering. Scale bar indicates 5 μm. (B) Proportion of halted MD4 B cells showing membrane ruffles on membranes bearing HEL at the specified density alone and with CXCL13. (C) DIC and fluorescent images for antigen, F-actin, and pMLCs of 2 representative fixed MD4 B cells in each case on CXCL13-coated membranes tethered with HEL (20 molecules/μm²). Scale bar indicates 2 μm. (D) Frequency of stopped MD4 B cells that show target membrane contact (IRM⁺) and extend ruffles (estimated by DIC) on CXCL13-coated membranes with tethered HEL after treatment with 0.1% DMSO (carrier), 0.5μM latrunculin A (LAT), 50μM blebbistatin (Blebb), or no treatment (none). All experiments were performed in the presence of ICAM-1 (150 molecules/μm²). Data in panels B and D represent the mean ± SEM of 4 experiments. Gray bar indicates not detected. *P < .05.