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Depletion of FOXP3+ regulatory T cells promotes hypercholesterolemia and atherosclerosis.Atherosclerosis is a chronic inflammatory disease promoted by hyperlipidemia. Several studies support FOXP3-positive regulatory T cells (Tregs) as inhibitors of atherosclerosis; however, the mechanism underlying this protection remains elusive. To define the role of FOXP3-expressing Tregs in atherosclerosis, we used the DEREG mouse, which expresses the diphtheria toxin (DT) receptor under control of the Treg-specific Foxp3 promoter, allowing for specific ablation of FOXP3+ Tregs. Lethally irradiated, atherosclerosis-prone, low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice received DEREG bone marrow and were injected with DT to eliminate FOXP3(+) Tregs. Depletion of Tregs caused a 2.1-fold increase in atherosclerosis without a concomitant increase in vascular inflammation. These mice also exhibited a 1.7-fold increase in plasma cholesterol and an atherogenic lipoprotein profile with increased levels of VLDL. Clearance of VLDL and chylomicron remnants was hampered, leading to accumulation of cholesterol-rich particles in the circulation. Functional and protein analyses complemented by gene expression array identified reduced protein expression of sortilin-1 in liver and increased plasma enzyme activity of lipoprotein lipase, hepatic lipase, and phospholipid transfer protein as mediators of the altered lipid phenotype. These results demonstrate that FOXP3(+) Tregs inhibit atherosclerosis by modulating lipoprotein metabolism.
Mouse cytomegalovirus infection overrules T regulatory cell suppression on natural killer cells.Cytomegalovirus establishes lifelong persistency in the host and leads to life threatening situations in immunocompromised patients. FoxP3+ T regulatory cells (Tregs) critically control and suppress innate and adaptive immune responses. However, their specific role during MCMV infection, especially pertaining to their interaction with NK cells, remains incompletely defined.
Regulatory T cells increase the avidity of primary CD8+ T cell responses and promote memory.Although regulatory T cells (T(regs)) are known to suppress self-reactive autoimmune responses, their role during T cell responses to nonself antigens is not well understood. We show that T(regs) play a critical role during the priming of immune responses in mice. T(reg) depletion induced the activation and expansion of a population of low-avidity CD8(+) T cells because of overproduction of CCL-3/4/5 chemokines, which stabilized the interactions between antigen-presenting dendritic cells and low-avidity T cells. In the absence of T(regs), the avidity of the primary immune response was impaired, which resulted in reduced memory to Listeria monocytogenes. These results suggest that T(regs) are important regulators of the homeostasis of CD8(+) T cell priming and play a critical role in the induction of high-avidity primary responses and effective memory.
Transient depletion of regulatory T cells in transgenic mice reactivates virus-specific CD8+ T cells and reduces chronic retroviral set points.Although chronic infections with viruses such as HIV and hepatitis C virus have been associated with regulatory T cell (Treg)-mediated suppression of virus-specific CD8(+) T-cell activity, no causal relationship between Tregs and chronic viral set points has been established. Using transgenic mice in which Tregs can be selectively ablated, we now show that transient depletion of Tregs during a chronic retroviral infection allows exhausted CD8(+) T cells to regain antiviral functions, including secretion of cytokines, production of cytotoxic molecules, and virus-specific cytolytic activity. Furthermore, short-term Treg ablation resulted in long-term reductions in chronic virus loads. These results demonstrate that Treg-mediated immunosuppression can be a significant factor in the maintenance of chronic viral infections and that Treg-targeted immunotherapy could be a valuable component in therapeutic strategies to treat chronic infectious diseases.