Vanessa Frodermann

A Modulatory Interleukin-10 Response to Staphylococcal Peptidoglycan Prevents Th1/Th17 Adaptive Immunity to Staphylococcus aureus

Toll-like receptor (TLR) 2 on antigen-presenting cells (APCs) enables these cells to recognize peptidoglycan-embedded lipopeptides and glycopolymers in the Staphylococcus aureus cell wall and mount an inflammatory response to this microbe. TLR2 signalling can also modulate immunity to S. aureus by inducing an interleukin (IL)-10 response in APCs. What determines the balance between proinflammatory and modulatory responses to S. aureus is unknown. We show that the modulatory IL-10 response preferentially occurs upon CD14- and CD36-independent TLR2 signaling, triggering PI3K activation, and is restricted to monocytes and monocyte-derived macrophages (MΦs). In contrast, monocyte-derived dendritic cells (DCs) produce mostly IL-12 and IL-23. The differential APC polarization induced by staphylococcal peptidoglycan translates into differential T helper responses: MΦs primarily trigger IL-10 and weak IL-17 responses, whereas DCs trigger a robust Th1/Th17 response. Exploitation of TLR2 signalling plasticity by S. aureus may explain the wide range of outcomes of human encounters with this microbe.

Differential effects of regulatory T cells on the initiation and regression of atherosclerosis

OBJECTIVE Regulatory T cells (Tregs) play an important role in the regulation of T cell-mediated immune responses through suppression of T cell proliferation and cytokine production. In atherosclerosis, a chronic autoimmune-like disease, an imbalance between pro-inflammatory cells (Th1/Th2) and anti-inflammatory cells (Tregs) exists. Therefore, increased Treg numbers may be beneficial for patients suffering from atherosclerosis. In the present study, we determined the effect of a vast expansion of Tregs on the initiation and regression of well-established lesions. METHODS AND RESULTS For in vivo Treg expansion, LDL receptor deficient (LDLr(-/-)) mice received repeated intraperitoneal injections of a complex of IL-2 and anti-IL-2 mAb. This resulted in a 10-fold increase in CD4(+)CD25(hi)Foxp3(+) T cells, which potently suppressed effector T cells ex vivo. During initial atherosclerosis, IL-2 complex treatment of LDLr(-/-) mice fed a Western-type diet reduced atherosclerotic lesion formation by 39%. The effect on pre-existing lesions was assessed by combining IL-2 complex treatment with a vigorous lowering of blood lipid levels in LDLr(-/-) mice. This did not induce regression of atherosclerosis, but significantly enhanced lesion stability. CONCLUSION Our data show differential roles for Tregs during atherosclerosis: Tregs suppress inflammatory responses and attenuate initial atherosclerosis development, while during regression Tregs can improve stabilization of the atherosclerotic lesions.

T-Cell Immunoglobulin and Mucin Domain 3 Acts as a Negative Regulator of Atherosclerosis

Objective—Atherosclerosis is a chronic autoimmune-like disease in which lipids and fibrous elements accumulate in the arterial blood vessels. T cells are present within atherosclerotic plaques, and their activation is partially dependent on costimulatory signals, which can either provide positive or negative signals that promote T-cell activation or limit T-cell responses, respectively. T-cell immunoglobulin and mucin domain 3 (Tim-3) is a coinhibitory type 1 transmembrane protein that affects the function of several immune cells involved in atherosclerosis, such as monocytes, macrophages, effector T cells, and regulatory T cells. In the present study, we determined the role of Tim-3 in the development of atherosclerosis. Approach and Results—Western-type diet–fed low-density lipoprotein receptor–deficient (LDLr−/−) mice were treated with an anti–Tim-3 antibody for 3 and 8 weeks. Anti–Tim-3 administration increased fatty streak formation with 66% and increased atherosclerotic plaque formation after 8 weeks with 35% in the aortic root and with 50% in the aortic arch. Furthermore, blockade of Tim-3 signaling increased percentages of circulating monocytes with 33% and lesional macrophages with 20%. In addition, anti–Tim-3 administration increased CD4+ T cells with 17%, enhanced their activation status, and reduced percentages of regulatory T cells with 18% and regulatory B cells with 37%. Conclusions—It is known that Tim-3 acts as a negative regulator of both innate and adaptive immune responses, and in the present study, we show that anti–Tim-3 treatment augments lesion development, accompanied by an increase in the number of monocytes/macrophages and CD4+ T cells and by decreased regulatory T cells and regulatory B cells.

Interference of the CD30–CD30L Pathway Reduces Atherosclerosis Development

Objective—Costimulatory molecules tightly control immune responses by providing positive signals that promote T-cell activation or by transducing inhibitory signals that limit T-cell responses. CD30 and CD30L are members of the tumor necrosis factor receptor superfamily and are involved in the activation and proliferation of T and B cells, which have been implicated in the initiation and progression of atherosclerosis. In the present study, we thus aimed to determine the role of the CD30–CD30L pathway in the development of atherosclerosis. Methods and Results—Western-type diet–fed low-density lipoprotein receptor–deficient mice were treated with an anti-CD30L antibody for 8 weeks, which resulted in a reduction of atherosclerotic lesion formation in the aortic root by 35%. Reduced numbers of adventitial CD3+ T cells were found in anti-CD30L–treated mice, whereas no differences were observed in collagen and macrophage content of the atherosclerotic lesions. B-cell and mast cell responses were also not affected on anti-CD30L treatment. Interestingly, splenocyte proliferation was reduced by 53%, whereas T-cell numbers were concomitantly reduced in anti-CD30L–treated mice compared with control mice. These data thus indicate that the CD30–CD30L pathway solely exerts its function via inhibition of T-cell responses. Conclusion—In the present study, we are the first to show that interruption of the CD30–CD30L pathway reduced initial atherosclerosis development by modulating T-cell function.

Neutrophil–macrophage cross-talk in acute myocardial infarction

This editorial refers to ‘Neutrophils orchestrate post-myocardial infarction healing by polarizing macrophages towards a reparative phenotype’, by M. Horckmans et al . on doi:10.1093/eurheartj/ehw002 Neutrophils are the first immune cells arriving at the site of infection or injury. These early responders are effective in fighting pathogens via several mechanisms: they phagocytose antibody- or complement-coated pathogens and kill them by NADPH oxidase-dependent mechanisms or antibacterial proteins that are released from granules into the phagosome. The content of these granules, i.e. various inflammatory mediators including neutrophil-derived lipocalin (NGAL), is also released to fight extracellular pathogens. Neutrophil extracellular traps (NETs), composed of chromatin, histones, and proteases, are yet another mechanism to capture and kill microorganisms.1 In sterile injury after ischaemia, danger-associated molecules released by necrotic tissues trigger the same Toll-like receptor-induced activation of neutrophils. After myocardial infarction (MI), neutrophils are the first to enter the damaged tissue in large numbers, and peak at day 1 after onset of ischaemia.2 While neutrophils initially help to clear cellular debris, their inflammatory mediators result in tissue damage and further leucocyte recruitment.3 Neutrophils may support recruitment and activation of Ly-6Chi monocytes,4 which dominate ischaemic tissue on days 1–4 after injury. Ly-6Chi monocytes are initially …

Agonistic Anti-TIGIT Treatment Inhibits T Cell Responses in LDLr Deficient Mice without Affecting Atherosclerotic Lesion Development

Objective Co-stimulatory and co-inhibitory molecules are mainly expressed on T cells and antigen presenting cells and strongly orchestrate adaptive immune responses. Whereas co-stimulatory molecules enhance immune responses, signaling via co-inhibitory molecules dampens the immune system, thereby showing great therapeutic potential to prevent cardiovascular diseases. Signaling via co-inhibitory T cell immunoglobulin and ITIM domain (TIGIT) directly inhibits T cell activation and proliferation, and therefore represents a novel therapeutic candidate to specifically dampen pro-atherogenic T cell reactivity. In the present study, we used an agonistic anti-TIGIT antibody to determine the effect of excessive TIGIT-signaling on atherosclerosis. Methods and Results TIGIT was upregulated on CD4+ T cells isolated from mice fed a Western-type diet in comparison with mice fed a chow diet. Agonistic anti-TIGIT suppressed T cell activation and proliferation both in vitro and in vivo. However, agonistic anti-TIGIT treatment of LDLr−/− mice fed a Western-type diet for 4 or 8 weeks did not affect atherosclerotic lesion development in comparison with PBS and Armenian Hamster IgG treatment. Furthermore, elevated percentages of dendritic cells were observed in the blood and spleen of agonistic anti-TIGIT-treated mice. Additionally, these cells showed an increased activation status but decreased IL-10 production. Conclusions Despite the inhibition of splenic T cell responses, agonistic anti-TIGIT treatment does not affect initial atherosclerosis development, possibly due to increased activity of dendritic cells.

Atherosclerosis: the interplay between lipids and immune cells.

Purpose of review Cardiovascular disease is the leading cause of mortality worldwide. The underlying cause of the majority of cardiovascular disease is atherosclerosis. In the past, atherosclerosis was considered to be the result of passive lipid accumulation in the vessel wall. However, todays picture of the pathogenesis of atherosclerosis is much more complex, with a key role for immune cells and inflammation in conjunction with hyperlipidemia, especially elevated (modified) LDL levels. Knowledge on immune cells and immune responses in atherosclerosis has progressed tremendously over the past decades, and the same is true for the role of lipid metabolism and the different lipid components. However, it is largely unknown how lipids and the immune system interact. In this review, we will describe the effect of lipids on immune cell development and function, and the effects of immune cells on lipid metabolism. Recent findings Recently, novel data have emerged that show that immune cells are affected, and behave differently in a hyperlipidemic environment. Moreover, immune cells have reported to be able to affect lipid metabolism. Summary In this review, we will summarize the latest findings on the interactions between lipids and the immune system, and we will discuss the potential consequences of these novel insights for future therapies for atherosclerosis.

Mesenchymal Stem Cells Reduce Murine Atherosclerosis Development

Mesenchymal stem cells (MSCs) have regenerative properties, but recently they were also found to have immunomodulatory capacities. We therefore investigated whether MSCs could reduce atherosclerosis, which is determined by dyslipidaemia and chronic inflammation. We adoptively transferred MSCs into low-density lipoprotein-receptor knockout mice and put these on a Western-type diet to induce atherosclerosis. Initially after treatment, we found higher levels of circulating regulatory T cells. In the long-term, overall numbers of effector T cells were reduced by MSC treatment. Moreover, MSC-treated mice displayed a significant 33% reduction in circulating monocytes and a 77% reduction of serum CCL2 levels. Most strikingly, we found a previously unappreciated effect on lipid metabolism. Serum cholesterol was reduced by 33%, due to reduced very low-density lipoprotein levels, likely a result of reduced de novo hepatic lipogenesis as determined by a reduced expression of Stearoyl-CoA desaturase-1 and lipoprotein lipase. MSCs significantly affected lesion development, which was reduced by 33% in the aortic root. These lesions contained 56% less macrophages and showed a 61% reduction in T cell numbers. We show here for the first time that MSC treatment affects not only inflammatory responses but also significantly reduces dyslipidaemia in mice. This makes MSCs a potent candidate for atherosclerosis therapies.

CD11b + Gr-1 + myeloid-derived suppressor cells reduce atherosclerotic lesion development in LDLr deficient mice

AIMS Myeloid-derived suppressor cells (MDSCs) form a heterogeneous population of cells composed of early myeloid progenitor cells and immature myeloid cells, which strongly suppress pro-inflammatory immune cells in inflammatory diseases. Currently, it is unknown whether MDSCs contribute to atherosclerosis, a chronic inflammatory disease in which accumulation of lipoproteins in the arterial wall activates the immune system causing abnormal vascular remodelling and vessel occlusion. Here, we investigated whether and how MDSCs contribute to the development of atherosclerosis. METHODS AND RESULTS We show that MDSCs arise in the bone marrow of LDLr(-/-) mice during atherosclerosis and strongly suppress proliferation of T cells. Adoptive transfer of MDSCs into both female and male LDLr(-/-) mice fed a Western-type diet (WTD) ameliorates atherosclerosis with 35%. We observed a 54% reduction in adventitial T cells, and more specifically, MDSCs suppress Th1 and Th17 cells. In addition, treatment with MDSCs reduces circulating pro-atherogenic B2 cells. We found two subsets of MDSCs in the bone marrow of hypercholesterolemic mice, monocytic and granulocytic MDSCs (mo- and gr-MDSCs, respectively), of which the percentage of mo-MDSCs significantly increased during WTD feeding. Moreover, mo-MDSCs completely abolished splenocyte proliferation, whereas gr-MDSCs were unable to suppress proliferation. Mechanistically, we show that MDSCs from atherosclerotic mice suppress T cells in an IFN-γ- and nitric oxide-dependent manner, which is associated with the action of mo-MDSCs. CONCLUSION This study demonstrates that MDSCs develop during atherosclerosis and reduce atherosclerosis via suppression of pro-inflammatory immune responses.

Oxidized Low-Density Lipoprotein–Induced Apoptotic Dendritic Cells as a Novel Therapy for Atherosclerosis

Modulation of immune responses may form a powerful approach to treat atherosclerosis. It was shown that clearance of apoptotic cells results in tolerance induction to cleared Ags by dendritic cells (DCs); however, this seems impaired in atherosclerosis because Ag-specific tolerance is lacking. This could result, in part, from decreased emigration of DCs from atherosclerotic lesions because of the high-cholesterol environment. Nonetheless, local induction of anti-inflammatory responses by apoptotic cell clearance seems to dampen atherosclerosis, because inhibition of apoptotic cell clearance worsens atherosclerosis. In this study, we assessed whether i.v. administration of oxLDL-induced apoptotic DCs (apopox-DCs) and, as a control, unpulsed apoptotic DCs could modulate atherosclerosis by inducing tolerance. Adoptive transfer of apopox-DCs into low-density lipoprotein receptor knockout mice either before or during feeding of a Western-type diet resulted in increased numbers of CD103+ tolerogenic splenic DCs, with a concomitant increase in regulatory T cells. Interestingly, both types of apoptotic DCs induced an immediate 40% decrease in Ly-6Chi monocyte numbers and a 50% decrease in circulating CCL2 levels, but only apopox-DC treatment resulted in long-term effects on monocytes and CCL2 levels. Although initial lesion development was reduced by 40% in both treatment groups, only apopox-DC treatment prevented lesion progression by 28%. Moreover, progressed lesions of apopox-DC–treated mice showed a robust 45% increase in collagen content, indicating an enhanced stability of lesions. Our findings clearly show that apoptotic DC treatment significantly decreases lesion development, but only apopox-DCs can positively modulate lesion progression and stability. These findings may translate into a safe treatment for patients with established cardiovascular diseases using patient-derived apopox-DCs.