ROLE OF ELAM-1 IN ADHESION OF MONOCYTES TO ACTIVATED HUMAN ENDOTHELIAL-CELLS

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-degrees-C, F(ab')2 fragments of 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-degrees-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-CD 18. The pattern of adhesion of monocytes to HUVEC, activated with TNF assessed at 4-degrees-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-degrees-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.