Among the cytokines secreted by Th1 cells, IL-18 appears to negatively regulate VSMC accumulation within atheroma lesions in ApoE−/− mice, supporting the notion that IL-18 is an important mediator of Th1-induced atherosclerosis (Mallat et al., 2001; Elhage et al., 2003). This evidence concerns the gene APOE and atherosclerosis.