Enhancement of L-selectin, but not P-selectin, bond formation frequency by convective flow.
L-selectin-mediated leukocyte rolling has been proposed to require a high rate of bond formation compared to that of P-selectin to compensate for its much higher off-rate. To test this hypothesis, a microbead system was utilized to measure relative L-selectin and P-selectin bond formation rates on their common ligand P-selectin glycoprotein ligand-1 (PSGL-1) under shear flow. Using video microscopy, we tracked selectin-coated microbeads to detect the formation frequency of adhesive tether bonds. From velocity distributions of noninteracting and interacting microbeads, we observed that tether bond formation rates for P-selectin on PSGL-1 decreased with increasing wall shear stress, from 0.14 +/- 0.04 bonds/microm at 0.2 dyn/cm(2) to 0.014 +/- 0.003 bonds/microm at 1.0 dyn/cm(2). In contrast, L-selectin tether bond formation increased from 0.017 +/- 0.005 bonds/microm at 0.2 dyn/cm(2) to 0.031 +/- 0.005 bonds/microm at 1.0 dyn/cm(2). L-selectin tether bond formation rates appeared to be enhanced by convective transport, whereas P-selectin rates were inhibited. The transition force for the L-selectin catch-slip transition of 44 pN/bond agreed well with theoretical models (Pereverzev et al. 2005. Biophys. J. 89:1446-1454). Despite catch bond behavior, hydrodymanic shear thresholding was not detected with L-selectin beads rolling on PSGL-1. We speculate that shear flow generated compressive forces may enhance L-selectin bond formation relative to that of P-selectin and that L-selectin bonds with PSGL-1 may be tuned for the compressive forces characteristic of leukocyte-leukocyte collisions during secondary capture on the blood vessel wall. This is the first report, to our knowledge, comparing L-selectin and P-selectin bond formation frequencies in shear flow.
Paschall
Christopher D
CD
Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia 22908, USA.
Guilford
William H
WH
Lawrence
Michael B
MB
D000268:Adhesiveness; D001665:Binding Sites; D003198:Computer Simulation; D019041:L-Selectin / Q000737:chemistry*; D008562:Membrane Glycoproteins / Q000737:chemistry*; D044085:Microfluidics / Q000379:methods*; D008956:Models, Chemical; D019007:P-Selectin / Q000737:chemistry*; D011485:Protein Binding; D033081:Shear Strength; D013314:Stress, Mechanical
D008562:Membrane Glycoproteins; D019007:P-Selectin; C084882:P-selectin ligand protein; D019041:L-Selectin