Affiliations: [a] Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, USA | [b] Department of Medicine, Division of Cardiovascular Medicine, School of Medicine, University of Virginia, Charlottesville, VA, USA
Correspondence:
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Address for correspondence: Michael B. Lawrence, Ph.D., Department of Biomedical Engineering, University of VA, P.O. Box 800759, 415 Lane Road, Charlottesville, VA 22908, USA. Tel.: +1 434 982 4269; Fax: +1 434 982 3870; E-mail: mbl2a@virginia.edu.
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.
