Adhesion of monocyte very late antigen-4 to endothelial vascular cell adhesion molecule-1 induces interleukin-1 beta-dependent expression of interleukin-6 in endothelial cells

In atheroma, T cell-derived interferon-gamma (INF-gamma) stimulates endothe lial cells and facilitates recruitment of monocytes. We investigated potent ial mechanisms by which these interactions could contribute to local and sy stemic inflammatory responses. Specifically, we analyzed the expression of interleukin (IL)-1 beta and IL-6 in both cell types after coculture, the re levant adhesion molecules in this interaction, and transcriptional control by NF-kappa B. We studied coculture of purified peripheral blood monocytes with human umbilical vein endothelial cells (HUVECs), which were stimulated with INF-gamma (10(6) U/L) to model the activated endothelium of atheroscl erotic lesions. Coculture of monocytes with activated HUVECs resulted in re lease of IL-1 beta (40.6 +/- 3 pg/24 h, P = 0.002) and IL-6 (46.6 +/- 7 ng/ 24 h, P = 0.0015). Electrophoretic mobility gel shift assay and Northern bl otting in each cell type separately revealed NF-kappa B activation in both cell types, IL-1 beta mRNA expression predominantly in monocytes, and IL-6 mRNA expression predominantly in HUVECs. The endothelial IL-6 release was I L-1-dependent, because it was suppressed by IL-1 receptor antagonist. Exper iments with blocking antibodies demonstrated that binding of monocyte very late antigen-4 (VLA-4) to endothelial vascular cell adhesion molecule-1 (VC AM-1) was necessary for the induction of IL-1 beta in monocytes. Binding of monocyte VLA-4 to endothelial VCAM-1 induces NF-kappa B activation in both cell types with expression and release of IL-1 beta by monocytes, which in turn stimulates endothelial release of IL-6. The beta(1)-integrin-mediated expression of IL-1 beta and IL-6 could contribute to local and systemic in flammatory reactions in atherosclerosis.