Objective— Regulatory T cells (Tregs) protect against atherosclerosis in experimental models, but their association with cardiovascular disease in humans remains to be elucidated. The aim of the present study was to determine whether circulating Tregs predict the development of acute cardiovascular events in humans. Methods and Results— The study cohort consisted of a random sample of participants (n=700), aged 68 to 73 years, from the Malmö Diet and Cancer Study. Mononuclear leukocytes, stored at −140 ○ C at the baseline investigation in 1991–1994, were thawed and Tregs, defined by the expression of FoxP3 in CD4+ T cells, were analyzed by flow cytometry. There was no detectable loss of cells during storage, and the viability of thawed leukocytes was 95%. A low fraction of both CD4+FoxP3+ and CD4+CD25+FoxP3+ T cells was associated with a higher release of proinflammatory cytokines from activated mononuclear leukocytes, and this association was strongest for CD4+FoxP3+ cells. Eighty-four coronary events and 66 strokes were registered during follow-up until December 31, 2008. In a Cox proportional hazard regression model adjusting for major risk factors, low levels of baseline CD4+FoxP3+ T cells were associated with an increased risk for the development of acute coronary events but not stroke. There were no associations between CD4+CD25+FoxP3+ T cells and development of an acute coronary event or stroke. Conclusion— This study provides prospective evidence for the role of Tregs in the development of myocardial infarction. The findings are in accordance with previous experimental studies and provide clinical support for a protective role of Tregs in atherosclerosis. The lack of association between Tregs and stroke may reflect the more heterogeneous cause of this disease.

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Objectives. Autoimmune responses against oxidized low-density lipoprotein are considered to play an important pro-inflammatory role in atherosclerosis and to promote disease progression. T-regulatory cells (Tregs) are immunosuppressive cells that have an important part in maintaining self-tolerance and protection against autoimmunity. We investigated whether aBp210, a prototype atherosclerosis vaccine based on a peptide sequence derived from apolipoprotein B, inhibits atherosclerosis through the activation of Tregs.Design. Six-week-old Apoe ) ⁄ ) mice were immunized with aBp210 and received booster immunizations 3 and 5 weeks later, as well as 1 week before being killed at 25 weeks of age.Results. At 12 weeks, immunized mice had increased expression of the Treg marker CD25 on circulating CD4 cells, and concanavalin A (Con A)-induced interferon-c, interleukin (IL)-4, and IL-10 release from splenocytes was markedly depressed. At 25 weeks, there was a fivefold expansion of splenic CD4+ CD25+ Foxp3 Tregs, a 65% decrease in Con Ainduced splenic T-cell proliferation and a 37% reduction in the development of atherosclerosis in immunized mice. Administration of blocking antibodies against CD25 neutralized aBp210-induced Treg activation as well as the reduction of atherosclerosis. Conclusions. The present findings demonstrate that immunization of Apoe) ⁄ ) mice with the apolipoprotein B peptide vaccine aBp210 is associated with activation of Tregs. Administration of antibodies against CD25 results in depletion of Tregs and blocking of the atheroprotective effect of the vaccine. Modulation in atherosclerosis-related autoimmunity by antigenspecific activation of Tregs represents a novel approach for treatment of atherosclerosis.