Atomic force microscopy measurement of leukocyte-endothelial interaction

Abstract

Leukocyte adhesion to vascular endothelium is a key initiating step in the pathogenesis of many inflammatory diseases. In this study, we present real-time force measurements of the interaction between monocytic human promyelocytic leukemia cells (HL-60) cells and a monolayer of human umbilical vein endothelial cells (HUVECs) by using atomic force microscopy (AFM). The detachment of HL-60-HUVEC conjugates involved a series of rupture events with force transitions of 40–100 pN. The integrated force of these rupture events provided a quantitative measure of the adhesion strength on a whole cell level. The AFM measurements revealed that HL-60 adhesion is heightened in the borders formed by adjacent HUVECs. The average force and mechanical work required to detach a single HL-60 from the borders of a tumor necrosis factor-α-activated HUVEC layer were twice as high as those of the HUVEC bodies. HL-60 adhesion to the monolayer was significantly reduced by a monoclonal antibody against β₁-integrins and partially inhibited by antibodies against selectins ICAM-1 and VCAM-1 but was not affected by anti-α_Vβ₃. Interestingly, adhesion was also inhibited in a dose-dependent manner (IC₅₀≈ 100 nM) by a cyclic arginine-glycine-aspartic acid (cRGD) peptide. This effect was mediated via interfering with the VLA-4-VCAM-1 binding. In parallel measurements, transmigration of HL-60 cells across a confluent HUVEC monolayer was inhibited by the cRGD peptide and by both anti-β₁and anti-α_Vβ₃antibodies. In conclusion, these data demonstrate the role played by β₁-integrins in leukocyte-endothelial adhesion and transmigration and the role played by α_Vβ₃in transmigration, thus underscoring the high efficacy of cRGD peptide in blocking both the adhesion and transmigration of monocytes.