CXCL13 activates signal transduction pathways involving Rap1 and RAPL. (A) Activation of Rap1 in CXCL13-stimulated B cells. B cells were stimulated with CXCL13 (30 nM) for the indicated times and subjected to a pull-down assay with Ral GDS-RBD. The amounts of GTP-Rap1 (top) and total Rap1 protein (bottom) were examined by Western blotting with an anti-Rap1 antibody. (B) Shear-resistant adhesion of wild-type (WT) and RAPL-deficient B cells to ICAM-1. Cells were stimulated with CXCL13 (100 nM) and allowed to bind ICAM-1. Shear-resistant B-cell adhesion (2 dyne/cm²) was examined by parallel flow chamber assay.