B-cell migration and IS formation in response to CXCL13 and antigen stimuli. Frequency of migration (A) and mean velocity (B) of 3-83 B cells on membranes with tethered p31 at different densities alone or with CXCL13. (C) Tracks of migratory 3-83 B cells in the presence of tethered p31 at the specified densities with CXCL13. (D) Representative DIC, fluorescent antigen, and IRM images at 30 minutes of naive 3-83 B cells settled on membranes bearing p31 at the indicated densities alone or with CXCL13. Scale bar indicates 5 μm. Frequency of IS formation estimated by fluorescence (E) and frequency (F) and area of B cell:membrane contacts estimated by IRM (G) 30 minutes after 3-83 B cells settling on membranes. (H) Total antigen molecules accumulated at the 3-83 IS established after 30 minutes on membranes with tethered p31 at the indicated densities alone or with CXCL13. All experiments were performed in the presence of ICAM-1 (150 molecules/μm²). Data in panels A, E, and F represent the means ± SEM of 4 experiments; data in panels B, C, and H correspond to the merge of 3 experiments; data of a representative experiment are shown in panel G. Gray bar indicates not detected; ns, not significant. *P < .05; **P < .001; ***P < .0001.