Molecular mechanisms of monocyte adhesion to interleukin-1β-stimulated endothelial cells under physiologic flow conditions

This study identifies multiple pathways used by monocytes to adhere to 4-hour interleukin-1β stimulated human umbilical vein endothelial cells under flow conditions. Physiologic shear stresses were simulated in a flow chamber with parallel plate geometry; quantitation of primary adhesion, secondary adhesion, and transmigration was performed using phase contrast videomicroscopy. Neuraminidase treatment of monocytes reduced primary interaction by 50%, whereas blocking L-selectin or very late antigen-4 showed significant but smaller effects (~ 30% inhibition). However, a combined treatment against all three pathways was able to reduce interaction by 80%. Blocking β₂ and α₄ integrin pathways together inhibited secondary/firm adhesion by 75%. Only 40% of firmly adherent monocytes transmigrated across the endothelial monolayer with significantly increased transmigration times when both β₂ and α₄ integrins were blocked. These results demonstrate that monocytes can use multiple receptors to interact with endothelial cells at both primary and secondary adhesion stages, and that these pathways have to be blocked simultaneously for maximum inhibition.