Inside-out activation of VLA-4 and LFA-1 adhesiveness by rapid chemokine signals under shear flow is lost in talin1-deficient B cells. (A) Frequency of attachments (transient or arrests) of WT and CD19Tln1^−/− spleen-derived B cells (talin null) to medium-density VCAM-1 or ICAM-1 triggered by either immobilized CXCL12 or CXCL13. Attachments were measured at a shear stress of 0.75 dyne/cm² (on VCAM-1) or 0.5 dyne/cm² (on ICAM-1). All adhesive interactions on VCAM-1 and ICAM-1 were blocked with either α₄ or α_L blocking mAbs, respectively. Results shown are the mean ± range in 2 fields of view from 4 independent experiments. **P < .05 for arrests of Tln1^−/− versus WT cells. (B) WT and Tln1^−/− B cells untreated or pretreated with PTX were settled for 2 minutes on tumor necrosis factor-α-stimulated bEnd.3 cells and then subjected to a shear stress of 2 dyne/cm² for 10 minutes. The fractions of settled cells remaining adherent at the indicated time points are shown for each experimental group. Where indicated, intact or PTX treated lymphocytes were incubated with a cocktail of α₄ and α_L blocking mAbs. (C) Frequency of arrests of WT or Tln1^−/− B cells on high-density VCAM-1 or ICAM-1 (500 sites/μm²) measured at a shear stress of 0.75 dyne/cm² or 0.5 dyne/cm², respectively, in 2 fields of view. Results are the mean values ± range in 2 fields of view from an experiment representative of 4 independent experiments. **P < .05.