Influence of cell deformation on leukocyte rolling adhesion in shear flow

Blood cell interaction with vascular endothelium is important in microcircu lation, where rolling adhesion of circulating leukocytes along the surface of endothelial cells is a prerequisite for leukocyte emigration under flow conditions. HL-60 cell rolling adhesion to surface-immobilized P-selectin i n shear flow was investigated using a side-view pow chamber, which permitte d measurements of cell deformation and cell-substrate contact length as wel l as cell rolling velocity. A two-dimensional model was developed based on the assumption that fluid energy input to a rolling cell was essentially di stributed into two parts: cytoplasmic viscous dissipation, and energy neede d to break adhesion bonds between the rolling cell and its substrate. The f low fields of extracellular fluid and intracellular cytoplasm were solved u sing finite element methods with a deformable cell membrane represented by an elastic ring. The adhesion energy loss was calculated based on receptor- ligand kinetics equations. It was found that, as a result of shear-flow-ind uced cell deformation, cell-substrate contact area under high wall shear st resses (20 dyn/cm(2)) could be as much as twice of that under low stresses (0.5 dyn/cm(2)). An increase in contact area may cause more energy dissipat ion to both adhesion bonds and viscous cytoplasm, whereas the fluid energy input may decrease due to the flattened cell shape. Our model predicts that leukocyte rolling velocity will reach a plateau as shear stress increases, which agrees with both in vivo and iii vitro experimental observations.