Enhancement of L-Selectin, but Not P-Selectin, Bond Formation Frequency by Convective Flow

• Published in: Biophysical journal Vol. 94; no. 3; pp. 1034 - 1045
• Main Authors: Paschall, Christopher D., Guilford, William H., Lawrence, Michael B.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.2008; Biophysical Society; The Biophysical Society
• Subjects: Adhesive bonding; Adhesiveness; Beads; Binding Sites; Bonding; Cell Biophysics; Cells; Computer Simulation; Convective flow; Frequencies; L-Selectin - chemistry; Leukocytes; Ligands; Membrane Glycoproteins - chemistry; Microfluidics - methods; Microorganisms; Models, Chemical; Molecules; P-Selectin - chemistry; Protein Binding; Shear flow; Shear Strength; Shear stress; Stress, Mechanical; Tethers; Velocity
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1529/biophysj.106.098707

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/μm at 0.2 dyn/cm2 to 0.014±0.003 bonds/μm at 1.0 dyn/cm2. In contrast, L-selectin tether bond formation increased from 0.017±0.005 bonds/μm at 0.2 dyn/cm2 to 0.031±0.005 bonds/μm at 1.0 dyn/cm2. 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.