INFLUENCE OF PRESSING FORCE ON ROLLING CHARACTERISTICS OF HL-60 CELL LINE ON A BUMPY SUBSTRATE MIMICKING THE ENDOTHELIUM TOPOGRAPHY
Atsushi Shirai1, Jean-Paul Rieu2, Ryota Sugimoto3, Daisuke Yoshino1
1Institute of Fluid Science, Tohoku University, Japan; 2Universite Claude Bernard Lyon 1, France; 3Graduate School of Biomedical Engineering, Australia
Neutrophils are known to roll on endothelium of postcapillary venules as the early event in their immune response. Numerous studies have been performed on the rolling characteristics of the neutrophils focusing on binding with selectins on the endothelium. In the postcapillary venules, axially accumulated erythrocytes which displace neutrophils toward the vessel wall and it would affect the rolling characteristics of the cells on bumpy surface of the endothelial cell layer. In this study, we focused on the correlative effects of the pressing force from the red blood cells and the surface topography of the endothelium on the rolling characteristics of neutrophils. For this purpose, we introduced an inclined centrifuge microscope system with which we can apply well-controlled pressing and driving forces to the cells. Motion of HL-60 cell line was observed under a variety of the pressing force on a PDMS substrate which has a hexagonal pattern which mimics surface topography of the endothelial cell layer. The substrate also has a stripe pattern for the comparison of the motion of the cells with the hexagonal pattern. We examined influence of the pressing force on the traceability of the cells on the patterns. We measured velocity of the HL-60 cells on the substrate varying the applied pressing force from 23.5 to 70.5 pN while a constant driving force of 30 pN was applied. Mean cell velocity in the direction of the driving force on the hexagonal pattern relative to that on the stripe pattern decreased and the relative circular variance of the instantaneous cell velocity vectors increased with the increase in the pressing force. Obtained result implies that the pressing force by the axially accumulated erythrocytes, together with the bumpy surface topography of the endothelium, helps neutrophils to bind with selectins which express along border of the endothelial cells.