EFFECTS OF RECIRCULATING FLOW ON U-937 CELL-ADHESION TO HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS

We used a sudden-expansion flow chamber to examine U-937 cell adhesion to unactivated and tumor necrosis factor (TNF)-alpha-activated human umbilical vein endothelial cells (HUVEC) in recirculating flow. For bo th unactivated and TNF-alpha-activated HUVEC, U-937 cells exhibited tr ansient arrests within similar to 150 mu m of flow reattachment. Few a rrests occurred directly at the reattachment site. U-937 cell rolling was not observed. At all other locations within the recirculation zone , U-937 cells did not exhibit transient arrests or rolling. TNF-alpha activation increased the frequency of U-937 cell arrests near reattach ment but did not change the median arrest duration. Numerically simula ted cell trajectories failed to predict attachment near the reattachme nt point. Deviations between experiment and theory may result from the nonspherical shape and deformability of U-937 cells. These results de monstrate that U-937 cell transient arrests occur preferentially in th e vicinity of the reattachment point in recirculating flow. Possible m echanisms for adhesion include low shear stress, curved streamlines, f luid velocity components normal to the endothelium, and formation of l arger contact areas.