The Influence of the Regulatory T Lymphocytes on Atherosclerosis

Abstract

Atherosclerosis is complex inflammatory disease of the arterial wall, in which T lymphocytes play a significant role.1 Since the recognition that T lymphocytes are present in human atherosclerotic plaque nearly 2 decades ago,2 research has focused on the functional importance of these cells in the atherosclerotic process. The majority of T lymphocytes in atherosclerotic lesions are CD4+ T-helper cells with a phenotype characteristic of the proinflammatory T-helper 1 (Th1) subset. These cells recognize specifically antigens that are produced in relative abundance in hypercholesterolemic individuals or in plaques including oxidatively modified LDL (Ox-LDL) and HSP60/65. The T cells are activated when macrophage or dendritic cells present these antigens to the T cells in plaques or lymphoid tissues. The Th1 cells produce inflammatory cytokines IFN-γ, tumor necrosis factor (TNF)-α, and membrane CD40-ligand, which amplify the immune response through activation of macrophages, vascular smooth muscle cells, and endothelial cells.1 See page 2691 Many mechanisms have evolved to maintain immunologic self-tolerance and to limit responses to foreign antigens. One of these mechanisms involves regulatory T cells (Treg) that actively suppress responses of effector T cells. The best- characterized Treg are the natural CD4+CD25+ Treg that mature in the thymus and comprise 5% to 10% of peripheral CD4+ T cells.3 Other surface markers expressed by Treg include CTLA-4 and GITR. FoxP3, a forkhead family transcription factor, is a lineage specification factor for Treg and plays a crucial role in their suppressive function.4 Natural Treg are generated during thymic development, but Treg are also induced in peripheral tissues during immune responses. Treg express antigen receptors typical of effector T cells and are presumably activated by peptide antigens presented by APCs. They also require interleukin (IL)-2 for development and survival. Once activated, Treg may suppress other T …