Figure 4.

Immobilized chemokine and PMA modulate VLA-4 tether properties through distinct mechanisms. Kinetics of formation and dissociation of transient VLA-4–mediated tethers on very low density VCAM at a shear stress of 0.5 dyn/cm². Effect of immobilized SDF-1 (A) or soluble PMA (B) on tether frequency and lifetime. (A) The duration of all tethers formed by equal number of Jurkat cells perfused for 1 min over sVCAM-1 (18 sites/μm²) alone or cocoated with SDF-1 at 2 μg/ml was determined, and the natural log of the tethers that remained bound after initiation of tethering was plotted against tether duration. (B) Effect of PMA treatment of Jurkat on the frequency and duration of Jurkat tethers to sVCAM-1 (36 sites/μm²). In A and B a first order dissociation fitting of tether duration is indicated by white symbols. Filled symbols denote longer tethers with high order dissociation kinetics. (C) Effect of immobilized SDF-1 and VCAM-1 density on frequency and duration of tethers formed by PBTLs interacting at a shear stress of 0.5 dyn/cm² with the indicated densities of sVCAM-1 coimmobilized together with either inactivated or intact SDF-1 at 2 μg/ml. Least square analysis values of linear plots are depicted in r² in A–C. Background tethering to HSA-coated substrate was 0.5% in A–C. Results are representative of three to four independent experiments.