Hydrodynamic Recruitment of Leukocytes Is Influenced by Adherent Cell Morphology

Abstract

Innate immunity depends on the coordinated activity of multiple leukocytes at or near the site of tissue injury. Previous numerical studies have shown that an adherent leukocyte can hydrodynamically recruit a free-stream leukocyte towards the endothelial surface. Using a computer model we created, we numerically investigated the hydrodynamic recruitment of circulating cells due to the presence of a nearby adherent deformed cell. For circulating cells positioned one diameter or more above the reactive surface and subsequently involved in a glancing (out-of-plane) collision with an adherent cell, the simulation indicated that the free-stream cell could be driven closer to the surface. This behavior was seen to depend, in part, on the offset glancing distance. Furthermore, for a deformed adherent cell a similar effect was observed, but beginning at smaller offset glancing distances. We also examined the binary interaction for a free-stream cell initially less than one diameter above the surface. For fixed offset glancing distances, the binary interaction with a more significantly deformed adherent cell resulted in enhanced recruiting effectiveness, as quantified by the time needed for the cell to descend to a height where receptor-ligand interactions were possible.