title: Cell-free rolling mediated by L-selectin and sialyl Lewis(x) reveals the shear threshold effect.
abstract: The selectin family of adhesion molecules mediates attachment and rolling of neutrophils to stimulated endothelial cells. This step of the inflammatory response is a prerequisite to firm attachment and extravasation. We have reported that microspheres coated with sialyl Lewis(x) (sLe(x)) interact specifically and roll over E-selectin and P-selectin substrates (Brunk et al., 1996; Rodgers et al 2000). This paper extends the use of the cell-free system to the study of the interactions between L-selectin and sLe(x) under flow. We find that sLe(x) microspheres specifically interact with and roll on L-selectin substrates. Rolling velocity increases with wall shear stress and decreases with increasing L-selectin density. Rolling velocities are fast, between 25 and 225 microm/s, typical of L-selectin interactions. The variability of rolling velocity, quantified by the variance in rolling velocity, scales linearly with rolling velocity. Rolling flux varies with both wall shear stress and L-selectin site density. At a density of L-selectin of 800 sites/microm(2), the rolling flux of sLe(x) coated microspheres goes through a clear maximum with respect to shear stress at 0.7 dyne/cm(2). This behavior, in which the maintenance and promotion of rolling interactions on selectins requires shear stress above a threshold value, is known as the shear threshold effect. We found that the magnitude of the effect is greatest at an L-selectin density of 800 sites/microm(2) and gradually diminishes with increasing L-selectin site density. Our study is the first to reveal the shear threshold effect with a cell free system and the first to show the dependence of the shear threshold effect on L-selectin site density in a reconstituted system. Our ability to recreate the shear threshold effect in a cell-free system strongly suggests the origin of the effect is in the physical chemistry of L-selectin interaction with its ligand, and largely eliminates cellular features such as deformability or topography as its cause.
authors.affiliation: Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: A W
authors.initials: AW
authors.lastname: Greenberg
authors.forename: D K
authors.initials: DK
authors.lastname: Brunk
authors.forename: D A
authors.initials: DA
authors.lastname: Hammer
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002448:Cell Adhesion / Q000502:physiology; D002465:Cell Movement / Q000502:physiology; D002474:Cell-Free System; D004730:Endothelium, Vascular / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D019041:L-Selectin / Q000502:physiology*; D051379:Mice; D008863:Microspheres; D009504:Neutrophils / Q000502:physiology; D009844:Oligosaccharides / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D000080506:Sialyl Lewis X Antigen
chemical_list: D009844:Oligosaccharides; D011993:Recombinant Fusion Proteins; D000080506:Sialyl Lewis X Antigen; D019041:L-Selectin