Cytokines Regulate Vascular Functions Related to Stability of the Atherosclerotic Plaque

The cytokines are multipotent mediators of inflammation and immunity that can affect key functions of vascular wall cells. Growing evidence suggests that cytokines participate as autocrine or paracrine mediators in atherogenesis, as cells in lesions can both produce and respond to these mediators. The functions of vascular wall cells regulated by cytokines may influence lesion initiation, progression, or complication. For example, cytokines can regulate the expression of adhesion molecules crucial to the recruitment of leukocytes to lesions, including vascular cell adhesion molecule-1 (VCAM-1). Cytokines such as interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) can regulate the production of monocyte chemoattractant protein-1 (MCP-1), a potential signal for directed migration of monocytes into the intima. Cytokines can also regulate genes that encode other growth factors and cytokines themselves. TNF-alpha can induce IL-1 mRNA in human endothelial (EC) and smooth-muscle cells (SMC). IL-1 and TNF-alpha can augment the production by vascular cells of macrophage-colony stimulating factor (M-CSF), which may promote growth and activation of mononuclear phagocytes. Cytokines can exert both pro-and antiatherogenic actions. Activated T cells in human atheroma may secrete the lymphokine IFN-gamma, an inhibitor of SMC proliferation. Cytokines influence vasomotor tone in arteries, e.g., by inducing a form of nitric oxide synthase, the enzyme that synthesizes the vasodilatory nitric oxide radical. The cytokines also modulate endothelial functions that govern the formation and stability of blood thrombi. Finally, in the late stages of the disease, matrix metalloproteinases derived from macrophages or smooth-muscle cells themselves may contribute to weakening of the fibrous cap in the vulnerable shoulder area, promoting plaque rupture and occlusive thrombosis, culminating in the dramatic clinical manifestations of atherosclerosis, including myocardial infarction and stroke. Thus, cytokines can influence multiple aspects of atherogenesis and provide new and interesting targets for therapeutic intervention.