Upregulated adhesion molecule and cytokine expression on endothelial cells and infiltrating inflammatory cells occur in most vasculitis syndromes. These observations suggest that vasculitis is associated with pathologic activation of normal immune cell cytokine cascades. Abnormal expression of adhesion molecules and cytokines in vascular endothelium is a manifestation of endothelial dysfunction that can be triggered by a variety of stimuli, including infectious agents, immune complexes, and antiendothelial cell antibodies. Dysregulated adhesion molecule expression, uncontrolled inflammation, thrombosis, and vessel occlusion lead to the clinical manifestations of vasculitis.