Circulating white blood cells adhere to endothelium near an infection site; this occurs because infection causes ligands to be expressed on activated endothelium. Initially, a white blood cell rolls on the substrate, but eventually forms a firm adhesion, allowing it to crawl through the endothelial layer toward the infected tissue. A computational model of bond kinetics, cell deformability, and fluid dynamics was used to model the forces experienced by a cell during this process. The cell was modeled as a fluid-filled membrane; on its surface were hundreds of deformable microvilli—little fingers, ruffles in the white blood cell’s wrinkly membrane. These microvilli were deformable and their tips were decorated with PSGL-1 chemical receptors which bound to P-selectin ligands on the surface. Softer cells and cells subjected to higher fluid shear stress deformed more, and having more contact area, they formed more bonds and were able to resist more hydrodynamic load.

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