L-selectin dimerization enhances tether formation to properly spaced ligand

Area of Science:

• Cellular adhesion mechanisms
• Glycoprotein-ligand interactions
• Biophysics of cell tethering

Background:

• Selectins are cell adhesion molecules crucial for leukocyte trafficking.
• Selectin counterreceptors present carbohydrate ligands that bind selectins.
• L-selectin ligation is known to enhance cell rolling on endothelial surfaces.

Purpose of the Study:

• To investigate the role of L-selectin dimerization in leukocyte tethering and adhesion.
• To determine if L-selectin dimerization enhances tether formation or stabilization.
• To explore the influence of ligand density and shear stress on L-selectin-mediated adhesion.

Main Methods:

• Utilized monoclonal antibodies to induce L-selectin dimerization.
• Performed microkinetic analysis of individual cell tethers.
• Tested L-selectin binding to purified physiological ligands and glycopeptides.
• Investigated the effect of epidermal growth factor domain substitution.
• Assessed tethering under varying ligand densities and shear stress conditions.

Main Results:

• L-selectin dimerization significantly enhanced leukocyte tethering to purified ligands.
• Enhanced tethering resulted from increased tether formation, not stabilization.
• Dimerization's effect on adhesion was dependent on ligand density threshold.
• Epidermal growth factor domain substitution enhanced tether formation independently of ligand density.
• Elevated shear stress restored sensitivity to L-selectin dimerization at low ligand densities.

Conclusions:

• L-selectin dimerization promotes leukocyte tethering by increasing initial tether formation, especially with clustered ligands.
• Shear stress plays a critical role in augmenting L-selectin-mediated adhesion by increasing effective ligand density.
• The epidermal growth factor domain influences intrinsic ligand binding properties of L-selectin.