title: Regulation of L-selectin-dependent hydrodynamic shear thresholding by leukocyte deformability and shear dependent bond number.
abstract: BACKGROUND
  During inflammation leukocyte attachment to the blood vessel wall is augmented by capture of near-wall flowing leukocytes by previously adherent leukocytes. Adhesive interactions between flowing and adherent leukocytes are mediated by L-selectin and P-selectin Glycoprotein Ligand-1 (PSGL-1) co-expressed on the leukocyte surface and ultimately regulated by hydrodynamic shear thresholding.
  
  
  OBJECTIVE
  We hypothesized that leukocyte deformability is a significant contributory factor in shear thresholding and secondary capture.
  
  
  METHODS
  Cytochalasin D (CD) was used to increase neutrophil deformability and fixation was used to reduce deformability. Neutrophil rolling on PSGL-1 coated planar surfaces and collisions with PSGL-1 coated microbeads were analyzed using high-speed videomicroscopy (250 fps).
  
  
  RESULTS
  Increased deformability led to an increase in neutrophil rolling flux on PSGL-1 surfaces while fixation led to a decrease in rolling flux. Abrupt drops in flow below the shear threshold resulted in extended release times from the substrate for CD-treated neutrophils, suggesting increased bond number. In a cell-microbead collision assay lower flow rates were correlated with briefer adhesion lifetimes and smaller adhesive contact patches.
  
  
  CONCLUSIONS
  Leukocyte deformation may control selectin bond number at the flow rates associated with hydrodynamic shear thresholding. Model analysis supported a requirement for both L-selectin catch-slip bond properties and multiple bond formation for shear thresholding.
authors.affiliation: Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, USA.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Paschall
authors.affiliation: Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, USA.|Department of Medicine, Division of Cardiovascular Medicine, School of Medicine, University of Virginia, Charlottesville, VA, USA.
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Klibanov
authors.affiliation: Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, USA.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Lawrence
mesh_terms: D002460:Cell Line; D015638:Cytochalasin D / Q000737:chemistry / Q000494:pharmacology; D018056:Hemorheology; D006801:Humans; D057446:Hydrodynamics; D019041:L-Selectin / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism; D018715:Microscopy, Video; D009504:Neutrophils / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D033081:Shear Strength
chemical_list: D008562:Membrane Glycoproteins; C084882:P-selectin ligand protein; D019041:L-Selectin; D015638:Cytochalasin D
keywords: PSGL-1; Selectin; inflammation; mechanokinetics; neutrophil; rolling