CD154-stimulated GM-CSF release by vascular smooth muscle cells elicits monocyte activation--role in atherogenesis

During the early phase of atherosclerosis, T cells and monocytes attach to and migrate through the endothelium into the vessel wall. To provide an insight into the potential cross talk between T cells and smooth muscle cells (SMC) in atherogenesis, we investigated changes in gene expression caused by CD40 ligation in cultured vascular SMC and their consequences for monocyte activation. CD40 expression in human-cultured SMC was induced by 24-h treatment with tumor necrosis factor-alpha plus interferon-gamma followed by 12-h exposure to mouse myeloma cells stably expressing human CD154 or the corresponding control cells. DNA microarray analysis (Affymetrix HG-U952A chip) indicated 33 up-regulated genes in three individual experiments of which 19 encoded pro-inflammatory adhesion molecules, cytokines, chemokines, and receptors. One functional consequence of this change in gene expression was an activation of transformed human promonocytic-1 monocytes exposed to the conditioned medium of the stimulated SMC. Subsequent antibody neutralization experiments identified granulocyte-macrophage colony-stimulating factor (GM-CSF) as the SMC-derived cytokine responsible for this effect. Thus, vascular SMC-like endothelial cells appear to contribute to the maintenance of an inflammatory response in the atherosclerotic vessel wall upon CD40-CD154 co-stimulation. Among 19 up-regulated pro-inflammatory gene products, GM-CSF plays an important role in SMC-dependent monocyte activation.