CXCL13/CXCR5 signaling enhances BCR-triggered B-cell activation by shaping cell dynamics.

Continuous migration of B cells at the follicle contrasts with their stable arrest after encounter with antigen. Two main ligand/receptor pairs are involved in these cell behaviors: the chemokine CXCL13/chemokine receptor CXCR5 and antigen/BCR. Little is known regarding the interplay between CXCR5 and BCR signaling in the modulation of B-cell dynamics and its effect on B-cell activation. We used a 2-dimensional model to study B-cell migration and antigen recognition in real time, and found that BCR signaling strength alters CXCL13-mediated migration, leading to a heterogeneous B-cell behavior pattern. In addition, we demonstrate that CXCL13/CXCR5 signaling does not impair BCR-triggered immune synapse formation and that CXCR5 is excluded from the central antigen cluster. CXCL13/CXCR5 signaling enhances BCR-mediated B-cell activation in at least 2 ways: (1) it assists antigen gathering at the synapse by promoting membrane ruffling and lymphocyte function-associated antigen 1 (LFA-1)-supported adhesion, and (2) it allows BCR signaling integration in motile B cells through establishment of LFA-1-supported migratory junctions. Both processes require functional actin cytoskeleton and non-muscle myosin II motor protein. Therefore, the CXCL13/CXCR5 signaling effect on shaping B-cell dynamics is an effective mechanism that enhances antigen encounter and BCR-triggered B-cell activation.