Role of ELAM‐1 in Adhesion of Monocytes to Activated Human Endothelial Cells

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Abstract
The role of ELAM-1 in the adhesion of monocytes to HUVEC, activated for 4 h with TNF, was studied using MoAb ENA2 directed against ELAM-1. In a standard adhesion assay at 37 C, F(ab')2 fragments of f ENA2 did not, or weakly inhibited adhesion. When metabolic activity of the monocytes was reduced by (i)fixing the monocytes, (ii) performing the adhesion assay at 4°C, and (iii) combining the forementioned conditions, the adhesion of the monocytes was strongly blocked by ENA2 and less effective or not by MoAb IB4 anti-CD18. The pattern of adhesion of monocytes to HUVEC, activated with TNF assessed at 4°C. paralleled ELAM-1 expression on the endothelial cells. Maximal inhibitory effect of ENA2 on adhesion was shown 5 h after activation of HUVEC, at which ELAM-1 expression was also maximal. Adhesion assessed at 37°C remained enhanced for at least 24 h, whereas the inhibitory effect of ENA2 followed ELAM-1 expression. Specific involvement of ELAM-1 was also confirmed using ELAM-1 transfected COS cells. These results indicated that monocytes express a counter structure for ELAM-1 and that this counter structure is involved in adhesion.