Cross-linking of CD14 molecules on monocytes results in a CD11/CD18- and ICAM-1-dependent adherence to cytokine-stimulated human endothelial cells.

The myeloid differentiation protein CD14 that is expressed on the surface of mature monocytes contributes to the adherence of monocytes to cytokine-stimulated monolayers of human macrovascular endothelial cells (EC). It has also been observed that the initial adherence of monocytes to cultured cytokine-stimulated EC eventually results in an ICAM-1- and LFA-1 (CD11a/CD18)-dependent adherence, which coincides with stretching and lateral migration of the monocytes over the surface of EC. Recently, it was reported that CD14 mediates monocyte activation and can induce a change in the avidity of CD11a/CD18 for its ligand ICAM-1. The aim of the present study was to investigate whether activation of monocytes by CD14 elicits a CD11/CD18-dependent adhesion of monocytes to ICAM-1 on rIL-1 alpha-stimulated EC. Incubation of monocytes with murine anti-CD14 mAb alone did not mobilize intracellular calcium but the subsequent addition of F(ab')2 anti-mouse Ig, which caused cross-linking of CD14 on the surface of monocytes, induced a transient rise in cytosolic free calcium concentration and enhanced the percentage monocytes that adhered to monolayers of macrovascular venous EC stimulated with rIL-1 alpha for 24 h, but not to nonstimulated EC. The elevated adhesion was decreased with monocytes were preincubated with staurosporine, an inhibitor of intracellular protein kinase activity and was markedly inhibited by mAb against the common beta 2-subunit (CD18) of the CD11/CD18 molecules on monocytes and by mAb against ICAM-1 on 24-h rIL-1 alpha-stimulated venous EC. These studies provide evidence for the hypothesis that the binding of monocytes via CD14 to rIL-1 alpha-stimulated EC generates an intracellular response in monocytes and triggers an adhesion mechanism that allows CD11/CD18 molecules on monocytes to bind to ICAM-1 on EC.