507b Mechanical Shedding of L-Selectin from the Leukocyte Surface: Theory and Experiment

Dooyoung Lee1, Kelly E. Caputo2, Daniel A. Hammer1, and Michael R. King3. (1) Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 South 33rd St, Philadelphia, PA 19104, (2) Chemical and Biomolecular Engineering, University of Pennsylvania, 311A Towne Building, 220 South 33rd St, Philadelphia, PA 19104, (3) Biomedical Engineering, University of Rochester, 218 Goergen Hall, RC 270168, Rochester, NY 14627

L-selectin-mediated leukocyte rolling is a key initial step in the multistep leukocyte adhesion cascade in blood. We have previously shown that constitutive L-selectin is cleaved from the neutrophil surface during rolling on a sialyl Lewis x-coated planar surface under physiological shear flow without the addition of exogenous stimuli. Based on the experimental work, we have extended the Adhesive Dynamics simulation of L-selectin-mediated cell rolling by incorporating the shear-dependent mechanical shedding of L-selectin. Utilizing the Bell model to describe a shedding rate which presumably increases exponentially with force, we were able to recreate the characteristics of L-selectin-mediated neutrophil rolling observed in flow experiments. First, the rolling velocity was found to increase during rolling due to mechanical shedding of L-selectin. The number of L-selectin shed during rolling depends strongly on the shear stress applied. When most of the L-selectin located on the tips of deformable microvilli was cleaved by force exerted on the L-selectin bonds, the cell detached from the reactive plane to join the free stream as observed in experiments. In summary, we showed through detailed computer simulations that the force-dependent shedding of L-selectin could fully explain the rolling behavior of neutrophils mediated by L-selectin in vitro.