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.

Atherosclerosis is a chronic inflammatory disease that is initiated by the retention and accumulation of cholesterol-containing lipoproteins, particularly low-density lipoprotein, in the artery wall. In the arterial intima, lipoprotein components that are generated through oxidative, lipolytic, and proteolytic activities lead to the formation of several danger-associated molecular patterns, which can activate innate immune cells as well as vascular cells. Moreover, self- and non-self-antigens, such as apolipoprotein B-100 and heat shock proteins, can contribute to vascular inflammation by triggering the response of T and B cells locally. This process can influence the initiation, progression, and stability of plaques. Substantial clinical and experimental data support that the modulation of adaptive immune system may be used for treating and preventing atherosclerosis. This may lead to the development of more selective and less harmful interventions, while keeping host defense mechanisms against infections and tumors intact. Approaches such as vaccination might become a realistic option for cardiovascular disease, especially if they can elicit regulatory T and B cells and the secretion of atheroprotective antibodies. Nevertheless, difficulties in translating certain experimental data into new clinical therapies remain a challenge. In this review, we discuss important studies on the function of T- and B-cell immunity in atherosclerosis and their manipulation to develop novel therapeutic strategies against cardiovascular disease.

Summary: Microvesicles are members of the family of extracellular vesicles shed from the plasma membrane of activated or apoptotic cells. Microvesicles were initially characterised by their pro-coagulant activity and described as “microparticles”. There is mounting evidence revealing a role for microvesicles in intercellular communication, with particular relevance to hemostasis and vascular biology. Coupled with this, the potential of microvesicles as meaningful biomarkers is under intense investigation. This Position Paper will summarise the current knowledge on the mechanisms of formation and composition of microvesicles of endothelial, platelet, red blood cell and leukocyte origin. This paper will also review and discuss the different methods used for their analysis and quantification, will underline the potential biological roles of these vesicles with respect to vascular homeostasis and thrombosis and define important themes for future research.

Immune responses to oxidized low-density lipoprotein (oxLDL) are proposed to be important in atherosclerosis. To identify the mechanisms of recognition that govern T cell responses to LDL particles, we generated T cell hybridomas from human ApoB100 transgenic (huB100tg) mice that were immunized with human oxLDL. Surprisingly, none of the hybridomas responded to oxidized LDL, only to native LDL and the purified LDL apolipoprotein ApoB100. However, sera from immunized mice contained IgG antibodies to oxLDL, suggesting that T cell responses to native ApoB100 help B cells making antibodies to oxLDL. ApoB100 responding CD4+ T cell hybridomas were MHC class II–restricted and expressed a single T cell receptor (TCR) variable (V) β chain, TRBV31, with different Vα chains. Immunization of huB100tgxLdlr−/− mice with a TRBV31-derived peptide induced anti-TRBV31 antibodies that blocked T cell recognition of ApoB100. This treatment significantly reduced atherosclerosis by 65%, with a concomitant reduction of macrophage infiltration and MHC class II expression in lesions. In conclusion, CD4+ T cells recognize epitopes on native ApoB100 protein, this response is associated with a limited set of clonotypic TCRs, and blocking TCR-dependent antigen recognition by these T cells protects against atherosclerosis.

Adaptive immunity has a major impact on atherosclerosis, with pro- and anti-atherosclerotic effects exerted by different subpopulations of T cells. Transforming growth factor–β (TGF-β) may promote development either of anti-atherosclerotic regulatory T cells or of T helper 17 (T_H17) cells, depending on factors in the local milieu. We have addressed the effect on atherosclerosis of enhanced TGF-β signaling in T cells. Bone marrow from mice with a T cell–specific deletion of Smad7, a potent inhibitor of TGF-β signaling, was transplanted into hypercholesterolemic Ldlr^−/− mice. Smad7-deficient mice had significantly larger atherosclerotic lesions that contained large collagen-rich caps, consistent with a more stable phenotype. The inflammatory cytokine interleukin-6 (IL-6) was expressed in the atherosclerotic aorta, and increased mRNA for IL-17A and the T_H17-specific transcription factor RORγt were detected in draining lymph nodes. Treating Smad7-deficient chimeras with neutralizing IL-17A antibodies reversed stable cap formation. IL-17A stimulated collagen production by human vascular smooth muscle cells, and RORγt mRNA correlated positively with collagen type I and α-smooth muscle actin mRNA in a biobank of human atherosclerotic plaques. These data link IL-17A to induction of a stable plaque phenotype, could lead to new plaque-stabilizing therapies, and should prompt an evaluation of cardiovascular events in patients treated with IL-17 receptor blockade.

Objective— Atherosclerosis is an inflammatory disease. Autoimmune responses to low-density lipoproteins (LDL) contribute to its progression, whereas immunization with LDL may induce atheroprotective or proatherogenic responses. The objective of this study was to develop an atheroprotective vaccine by targeting a peptide of the LDL protein constituent apolipoprotein B-100 (apoB-100) to the nasal mucosa to induce a protective mucosal immune response. Methods and Results— A peptide comprising amino acids 3136 to 3155 of apoB-100 (p210) was fused to the B subunit of cholera toxin (CTB), which binds to a ganglioside on mucosal epithelia. The effect of nasal administration of the p210-CTB fusion protein on atherogenesis was compared with that of an ovalbumin peptide fused to CTB and with untreated controls. Immunization with p210-CTB for 12 weeks caused a 35% reduction in aortic lesion size in Apoe ^−/− mice. This effect was accompanied by induction of regulatory T cells that markedly suppressed effector T cells rechallenged with apoB-100 and increased numbers of interleukin (IL)-10 ⁺ CD4 ⁺ T cells. Furthermore, a peptide-specific antibody response was observed. Atheroprotection was also documented in apoe ^−/− mice lacking functional transforming growth factor-β receptors on T cells. Conclusion— Nasal administration of an apoB-100 peptide fused to CTB attenuates atherosclerosis and induces regulatory Tr1 cells that inhibit T effector responses to apoB-100.