CXCR5 distribution at the contact site of migratory B cells and at the B-cell IS. (A) Representative DIC and fluorescence images at the contact site of a typical migratory A20 B cell in the absence of tethered antigen at the indicated times. White arrows indicate aggregates of CXCR5-GFP at the tips of the leading edge. Scale bar indicates 5 μm. (B) DIC and fluorescent images of a representative A20 B cell forming the IS after surrogate antigen (anti-κ mAb) recognition on the membrane. Scale bar indicates 5 μm. (C) Profiles of relative mean fluorescence distribution of CXCR5-GFP (green line) and antigen (red line) at the contact site of the A20 B cell with the membrane at 0 minutes (left; white arrow at bottom left panel in B) and 12 minutes (right; white arrow at bottom right panel in B). (D) Serial z-stack sections taken every 2 μm of a representative A20 B cell with an established IS on membranes with tethered surrogate antigen. Scale bar indicates 2 μm. All experiments were performed in the presence of ICAM-1 (150 molecules/μm²).