Resident Memory T Cells in the Atherosclerotic Lesion Associate With Reduced Macrophage Content and Increased Lesion Stability

BACKGROUND

Tissue resident memory T (TRM) cells are a T-cell subset that resides at the site of prior antigen recognition to protect the body against reoccurring encounters. Besides their protective function, TRM cells have also been implicated in inflammatory disorders. TRM cells are characterized by the expression of CD69 and transcription factors Hobit (homolog of Blimp-1 [B lymphocyte-induced maturation protein 1] in T cells) and Blimp-1. As the majority of T cells in the arterial intima expresses CD69, TRM cells may contribute to the pathogenesis of atherosclerosis as well. Here, we aimed to assess the presence and potential role of TRM cells in atherosclerosis.

METHODS

To identify TRM cells in human atherosclerotic lesions, a single-cell RNA-sequencing data set was interrogated, and T-cell phenotypes were compared with that of integrated predefined TRM cells. The presence and phenotype of TRM in atherosclerotic lesions was corroborated using a mouse model that enabled tracking of Hobit-expressing TRM cells. To explore the function of TRM cells during atherogenesis, RAG1-/- (RAG1 deficient) LDLr-/- (low-density lipoprotein receptor knockout) mice received a bone marrow transplant from HobitKO/CREBlimp-1flox/flox mice, which exhibit abrogated TRM cell formation, whereafter the mice were fed a Western-type diet for 10 weeks.

RESULTS

Human atherosclerotic lesions contained T cells that exhibited a TRM cell-associated gene signature. Moreover, a fraction of these T cells clustered together with predefined TRM cells upon integration. The presence of Hobit-expressing TRM cells in the atherosclerotic lesion was confirmed in mice. These lesion-derived TRM cells were characterized by the expression of CD69 and CD49α. Moreover, we demonstrated that this small T-cell subset significantly affects lesion composition, by reducing the amount of intralesional macrophages and increasing collagen content.

CONCLUSIONS

TRM cells, characterized by the expression of CD69 and CD49α, constitute a minor population in atherosclerotic lesions and are associated with increased lesion stability in a Hobit and Blimp-1 knockout mouse model.

Cardiovascular risk factors: The effects of ageing and smoking on the immune system, an observational clinical study

Currently immunomodulatory compounds are under investigation for use in patients with cardiovascular disease, caused by atherosclerosis. These trials, using recurrent cardiovascular events as endpoint, require enrollment of large patient groups. We investigated the effect of key risk factors for atherosclerosis development, ageing and smoking, on the immune system, with the objective to identify biomarkers differentiating between human populations, and potentially serving as endpoints for future phase 1B trials with immunomodulatory compounds. Blood was collected from young healthy volunteers (aged 18-25 years, n=30), young smokers (18-25 years, n=20), elderly healthy volunteers (>60 years, n=20), heavy smokers (>45 years, 15 packyears, n=11) and patients with stable coronary artery disease (CAD) (>60 years, n=27). Circulating immune cell subsets were characterized by flow cytometry, and collected plasma was evaluated by proteomics (Olink). Clear ageing effects were observed, mostly illustrated by a lower level in CD8⁺ and naïve CD4⁺ and CD8⁺ T cells, with an increase in CD4⁺ and CD8⁺ effector memory T cells in elderly healthy volunteers compared to young healthy volunteers. Heavy smokers showed a more inflammatory cellular phenotype, especially a shift in Th1/Th2 ratio: higher Th1 and lower Th2 percentages compared to young healthy volunteers. A significant decrease in circulating atheroprotective oxLDL-specific IgM was found in patients with CAD compared to young healthy volunteers. Elevated pro-inflammatory and chemotactic proteins TREM1 and CCL11 were observed in elderly volunteers compared to young volunteers. In addition, heavy smokers had an increase in pro-inflammatory cytokine IL-6 and lysosomal protein LAMP3. These data show that ageing and smoking are associated with an inflammatory immunophenotype, and that heavy smokers or aged individuals may serve as potential populations for future clinical trials investigating immunomodulatory drugs targeted for cardiovascular disease.

APAC treatment limits collar-induced carotid atherosclerotic plaque development in apoE-/- mice

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Dutch Heart Foundation

Introduction and aim: Mimics of mast cell-derived heparin proteoglycans (HEP-PG) can be tailored to molecules carrying both antiplatelet and anticoagulant properties. These dual antiplatelet and anticoagulant (APAC) constructs can also shield adhesion molecules such as P-selectin and VCAM-1 expressed by endothelial cells upon atherosclerosis development. We hypothesize that via this way, APAC prevents macrophage accumulation and lesion development. In this study, we therefore determined the efficacy of APAC in inhibiting atherosclerosis.

Methods

Male western-type diet fed apoE-/- mice were equipped with perivascular carotid artery collars to induce atherosclerosis. In this collar model, mRNA expression of adhesion molecules such as ICAM-1, VCAM-1, P-Selectin but also of Platelet Factor 4 (PF4) are significantly upregulated upon lesion development (all P<0.05 at 2 weeks after collar placement compared with control arteries). From lesion initiation, mice were treated with 0.2 mg/kg APAC or vehicle control (i.v, 3x per week, n=12-14 per group) for 2.5 weeks. At 5 weeks after collar placement, mice were sacrificed.

Results

APAC treatment did not affect body weight or plasma total cholesterol levels of the mice during the experiment. Interestingly, carotid artery plaque size was reduced by over 50% upon APAC treatment (APAC: 50±10*10E3 versus controls: 102±13*10E3 square µm; P<0.01). This observation was aligned with reduced plaque macrophage area (APAC: 20±5*10E3 versus controls: 33±5*10E3 square µm) and collagen content (APAC: 13±4*10E3 versus controls: 28±6*10E3 square µm; P<0.05).

Conclusion

We here show that APAC effectively inhibits atherosclerotic lesion development when administered during lesion initiation and may have potential as therapeutic agent to prevent atherosclerosis.

Brutons tyrosine kinase inhibition to suppress mast cell activation in atherosclerosis

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation

Aim

Acute cardiovascular diseases, such as myocardial infarction or stroke, are still a major cause of death in Western Society. The main underlying pathology of cardiovascular diseases is atherosclerosis, which is caused by the accumulation of lipids and inflammatory cells in the vessel wall, in so-called atherosclerotic plaques. Mast cells accumulate within these atherosclerotic plaques and activation of mast cells leads to the progression and destabilization of advanced plaques via the secretion of pro-inflammatory mediators and cytokines. Mast cells can be activated by various stimuli, of which crosslinking of the Fcε receptor I (FcεRI) with IgE-antigen complexes is best known. Bruton’s tyrosine kinase (BTK), a cytoplasmic nonreceptor tyrosine kinase, is involved in the downstream signaling of FcεRI-mediated mast cell activation and degranulation. Therefore, BTK might be an attractive target to interfere in the FcεRI-mediated mast cell activation pathway. In this study, we thus aimed to assess the effects of the BTK inhibitor ACP-196 on FcεRI-mediated mast cell activation, plaque progression and destabilization in an atherosclerotic mouse model.

Methods and Results

Male LDLr knockout mice, 7-11 weeks old, were treated with ACP-196 (25 mg/kg p.o., n=15) or control solvent (n=14) three times per week for eight weeks. During treatment, mice were fed a Western-type diet (WTD) to induce atherosclerotic plaque formation. During the experiment, plasma total cholesterol levels and body weight did not differ between the control and treatment group. After eight weeks, mice were sacrificed and hearts were isolated to determine atherosclerotic plaque size and stability in the aortic root by histology. Other immunological relevant tissues, such as aorta, spleen and mediastinal lymph nodes were harvested to examine mast cell activation status and other immune cells by flow cytometry. After eight weeks of ACP-196 treatment in LDLr knockout mice, a significant 59% reduction in the frequency of CD117+ FcεRI+ mast cells was observed in aortic plaques of ACP-196 treated mice (0.24±0.06%) compared to control mice (0.57±0.08%, p<0.05), while relative mast cell activation status was not affected. Additionally, ACP-196 treatment inhibited B cell maturation in the circulation, spleen, mediastinal lymph nodes and peritoneal cavity of LDLr knockout mice compared to control mice. However, these effects on immune cells did not translate into effects on atherosclerosis, as ACP-196 treatment (size:12.3±2%; collagen:14.5±1.9%) did not significantly affect atherosclerotic plaque size and collagen content when compared to control mice (size:11.5±1.4%; collagen: 13.6±1.5%).

Conclusions

Conclusively, these findings suggest that ACP-196 treatment leads to reduced migration of mast cells to the atherosclerotic plaques of LDLr knockout mice, but does not directly affect mast cell activation and initial atherosclerotic lesion development.

B cell depletion skews cd4+ t cell towards a pro-inflammatory phenotype in aged atherosclerotic mice

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Dutch Heart Foundation

ERA CVD

Aims

Aging is associated with changes in the composition and function of the immune system, such as decreased B cell numbers and reduced antibody responses (1). In addition, aging is related to an increased incidence of inflammatory diseases, such as the lipid-driven chronic inflammatory disease atherosclerosis, the main underlying cause of cardiovascular disease (2). B cells play a major role in atherosclerosis progression by antibody secretion, antigen presentation and T cell regulation. Different B cell subsets, with either proatherogenic or antiatherogenic properties, have been identified in atherosclerosis, but the impact of aging on B cells during atherosclerosis remains to be elucidated. In contrast to young atherosclerotic mice where few B cells are found within the plaque, single cell RNA sequencing and flow cytometry data from our group revealed that B cells are one of the most dominant leukocytes present in atherosclerotic aortas from naturally aged LDLr-/- mice. In this study, we aimed to gain further insights into the role of these aged B cells on T cell immunity in atherosclerosis by depleting B cells in aged atherosclerotic mice.

Methods and Results

Aged (85-95 weeks) atherosclerotic male LDLr-/- mice were kept on a chow diet for six weeks, during which the mice received 250 µg B cell-depleting anti-CD20 antibody (Genentech) (n=12) or 250 µg rat IgG2a isotype control (n=12) once a week intraperitoneally. Mice that received the anti-CD20 antibody showed effective B cell depletion in the blood and lymphoid organs, such as the spleen and lymph nodes, but also locally in the atherosclerotic plaque. In addition, B cell depleted mice showed a significant increase in the percentage of T-bet expressing CD4+ T cells in aortic plaques compared to control mice (αCD20: 25.05±2.88% vs. ctrl: 15.94±2.14%, p<0.05). Furthermore, the percentage of RORyt+ and IL-17+ CD4+ T cells in the spleen and heart draining lymph nodes was increased after B cell depletion, indicating a shift towards Th17 differentiation.

Conclusions

Collectively, we show that CD20+ B cell depletion in aged LDLr-/- mice skews CD4+ T cells towards a Th1 phenotype in the atherosclerotic plaque and towards a Th17 phenotype in lymphoid organs, suggesting a protective role for aged B cells in atherosclerosis. However, B cells are a heterogeneous population and further research should elucidate whether aged B cells exert a pro- or anti-atherogenic role. In conclusion, our results indicate that aged B cells have an important function in CD4+ T cell differentiation and could be attractive targets to combat age-related cardiovascular disease.

Granzyme B+ CD4+ T cells associate with an unstable plaque phenotype in advanced human atherosclerosis

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): The Dutch Heart Foundation

Cytotoxic CD4+ T cells have previously been found in peripheral blood of patients with coronary artery disease (1), however their occurrence in atherosclerotic plaques and their association with the pathophysiology of atherosclerosis has not been established.

Single-cell RNA sequencing was performed on human carotid atherosclerotic plaques of 18 patients to identify specific T cell populations (2). Next, human femoral and carotid atherosclerotic plaques (n=95) and matched blood samples (n=49) were analyzed by flow cytometry for the presence of CD4+GZMB+ T cells. Plaque morphology was assessed by Movat’s Pentachrome staining.

A distinct cytotoxic GZMB+ PRF1+ CD28- CD4+ T cell cluster was identified using single-cell RNA sequencing. Furthermore, flow cytometry analysis showed that the percentage of GZMB+CD4+ T cells was significantly elevated in plaque compared to blood (Blood: 12.17±2.0 vs. Plaque: 17.40±1.0; P=0.0002). Moreover, a significant positive correlation was observed between the percentage of GZMB+CD4+ T cells in blood versus plaque (P=0.031). In line with the proinflammatory character of these cells, we found a positive association of GZMB+CD4+ T cells (P=0.036) with necrotic core size, whereas no correlation was found with this subtype in the circulation.

In this study we have shown an enrichment of cytotoxic CD4+ T cells in atherosclerotic lesions, which positively correlate with necrotic core size. Future studies are aimed at elucidating the role of these cells in advanced atherosclerosis.

B- and T-lymphocyte attenuator stimulation protects against atherosclerosis by regulating follicular B cells

AIMS

The immune system is strongly involved in atherosclerosis and immune regulation generally leads to attenuated atherosclerosis. B- and T-lymphocyte attenuator (BTLA) is a novel co-receptor that negatively regulates the activation of B and T cells; however, there have been no reports of BTLA and its function in atherosclerosis or cardiovascular disease (CVD). We aimed to assess the dominant BTLA expressing leucocyte in CVD patients and to investigate whether BTLA has a functional role in experimental atherosclerosis.

METHODS AND RESULTS

We show that BTLA is primarily expressed on B cells in CVD patients and follicular B2 cells in low-density lipoprotein receptor-deficient (Ldlr-/-) mice. We treated Ldlr-/- mice that were fed a western-type diet (WTD) with phosphate-buffered saline, an isotype antibody, or an agonistic BTLA antibody (3C10) for 6 weeks. We report here that the agonistic BTLA antibody significantly attenuated atherosclerosis. This was associated with a strong reduction in follicular B2 cells, while regulatory B and T cells were increased. The BTLA antibody showed similar immunomodulating effects in a progression study in which Ldlr-/- mice were fed a WTD for 10 weeks before receiving antibody treatment. Most importantly, BTLA stimulation enhanced collagen content, a feature of stable lesions, in pre-existing lesions.

CONCLUSION

Stimulation of the BTLA pathway in Ldlr-/- mice reduces initial lesion development and increases collagen content of established lesions, presumably by shifting the balance between atherogenic follicular B cells and atheroprotective B cells and directing CD4+ T cells towards regulatory T cells. We provide the first evidence that BTLA is a very promising target for the treatment of atherosclerosis.

High LDL levels lessen bone destruction during antigen-induced arthritis by inhibiting osteoclast formation and function

Rheumatoid arthritis (RA) is a chronic inflammatory disease, characterized by severe joint inflammation and bone destruction as the result of increased numbers and activity of osteoclasts. RA is often associated with metabolic syndrome, whereby elevated levels of LDL are oxidized into oxLDL, which might affect osteoclastogenesis. In this study, we induced antigen-induced arthritis (AIA) in Apoe^-/- mice, which spontaneously develop high LDL levels, to investigate the effects of high LDL/oxLDL levels on osteoclast differentiation and bone destruction. Whereas basal levels of bone resorption were comparable between naive WT and Apoe^-/- mice, induction of AIA resulted in a significant reduction of bone destruction in Apoe^-/- mice as compared to WT controls. In line with that, the TRAP⁺ area on the cortical bone was significantly decreased. The absence of Apoe did affect neither the numbers of CD11b⁺Ly6C^high and CD11b^-/Ly6C^high osteoclast precursors (OCPs) in the BM of naïve mice nor their in vitro osteoclastogenic potential as indicated by comparable mRNA expression of osteoclast markers. Addition of oxLDL, but not LDL, to pre-osteoclasts from day 3 and mature osteoclasts from day 6 of osteoclastogenesis strongly reduced the number of TRAP⁺ osteoclasts and their resorptive capacity. This coincided with a decreased expression of various osteoclast markers. Interestingly, oxLDL significantly lowered the expression of osteoclast-associated receptor (Oscar) and the DNAX adaptor protein-12 encoding gene Tyrobp, which regulate the immunoreceptor tyrosine-based activation motif (ITAM) co-stimulation pathway that is strongly involved in osteoclastogenesis. Collectively, our findings suggest that under inflammatory conditions in the joint, high LDL levels lessen bone destruction during AIA, probably by formation of oxLDL that inhibits osteoclast formation and activity through modulation of the ITAM-signaling.

Lipocalin-2 contributes to experimental atherosclerosis in a stage-dependent manner

BACKGROUND AND AIMS

Lipocalin-2 (Lcn2) is a glycoprotein which can be secreted by immune cells. Several studies in humans have suggested Lcn2 can be used as a biomarker for the detection of unstable atherosclerotic lesions, partly as it is known to interact with MMP-9.

METHODS

In this study, we generated Ldlr^-/-Lcn2^-/- mice to assess the functional role of Lcn2 in different stages of atherosclerosis. Atherosclerotic lesions were characterized through histological analysis and myeloid cell populations were examined using flow cytometry.

RESULTS

We show that Ldlr^-/-Lcn2^-/- mice developed larger atherosclerotic lesions during earlier stages of atherosclerosis and had increased circulating Ly6C^hi inflammatory monocytes compared to Ldlr^-/- mice. Advanced atherosclerotic lesions from Ldlr^-/-Lcn2^-/- mice had decreased necrotic core area, suggesting Lcn2 deficiency may affect lesion stability. Furthermore, MMP-9 activity was diminished in plaques from Ldlr^-/-Lcn2^-/- mice.

CONCLUSIONS

Altogether, these findings suggest that Lcn2 deficiency promotes lesion growth in earlier stages of the disease while it decreases MMP-9 activity and necrotic core size in advanced atherosclerosis.

Heat-killed Staphylococcus aureus reduces atherosclerosis by inducing anti-inflammatory macrophages

BACKGROUND

Staphylococcus aureus cell wall components can induce IL-10 responses by immune cells, which may be atheroprotective. Therefore, in this study, we investigated whether heat-killed S. aureus (HK-SA) could inhibit the development of atherosclerosis.

METHODS

Atherosclerosis-susceptible LDL receptor-deficient mice were administered intraperitoneal HK-SA twice weekly and fed a Western-type diet for 6 weeks.

RESULTS

HK-SA administration resulted in a 1.6-fold increase in IL-10 production by peritoneal macrophages and splenocytes, and a 12-fold increase in serum IL-10 levels. Moreover, aortic plaque ICAM-1, VCAM-1 and CCL2 expression levels were significantly downregulated by on average 40%. HK-SA-treated mice had reduced numbers of inflammatory Ly-6C(hi) monocytes as well as Th1 and Th17 cells in the circulation and spleen, respectively. Attenuated leucocyte recruitment resulted in a significant inhibition of macrophage and T cell infiltration in atherosclerotic plaques, culminating in a significant 34% reduction in the development of atherosclerosis. To determine the effects of intraperitoneal HK-SA treatment, we stimulated macrophages with HK-SA in vitro. This resulted in a significant toll-like receptor 2 (TLR2)-dependent increase in IL-10, arginase-1, iNOS, TNF-α, PD-L1, CCL22 and indoleamine 2,3-dioxygenase expression. It was found that phosphoinositide 3-kinase crucially determined the balance of pro- and anti-inflammatory gene expression. The HK-SA-induced macrophage phenotype resembled M2b-like immunoregulatory macrophages.

CONCLUSIONS

We have shown that HK-SA treatment induces strong anti-inflammatory IL-10 responses by macrophages, which are largely dependent on TLR2 and PI3K, and protects against the development of atherosclerosis. Commensalism with S. aureus could thus reduce cardiovascular events.

The role of mast cells in atherosclerosis

Rupture of an atherosclerotic plaque is the major underlying cause of adverse cardiovascular events such as myocardial infarction or stroke. Therapeutic interventions should therefore be directed towards inhibiting growth of atherosclerotic lesions as well as towards prevention of lesion destabilization. Interestingly, the presence of mast cells has been demonstrated in both murine and human plaques, and multiple interventional murine studies have pointed out a direct role for mast cells in early and late stages of atherosclerosis. Moreover, it has recently been described that activated lesional mast cells correlate with major cardiovascular events in patients suffering from cardiovascular disease. This review focuses on the effect of different mast cell derived mediators in atherogenesis and in late stage plaque destabilization. Also, possible ligands for mast cell activation in the context of atherosclerosis are discussed. Finally, we will elaborate on the predictive value of mast cells, together with therapeutic implications, in cardiovascular disease.

Exendin-4 decreases liver inflammation and atherosclerosis development simultaneously by reducing macrophage infiltration

BACKGROUND AND PURPOSE

The aetiology of inflammation in the liver and vessel wall, leading to non-alcoholic steatohepatitis (NASH) and atherosclerosis, respectively, shares common mechanisms including macrophage infiltration. To treat both disorders simultaneously, it is highly important to tackle the inflammatory status. Exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist, reduces hepatic steatosis and has been suggested to reduce atherosclerosis; however, its effects on liver inflammation are underexplored. Here, we tested the hypothesis that exendin-4 reduces inflammation in both the liver and vessel wall, and investigated the common underlying mechanism.

EXPERIMENTAL APPROACH

Female APOE*3-Leiden.CETP mice, a model with human-like lipoprotein metabolism, were fed a cholesterol-containing Western-type diet for 5 weeks to induce atherosclerosis and subsequently treated for 4 weeks with exendin-4.

KEY RESULTS

Exendin-4 modestly improved dyslipidaemia, but markedly decreased atherosclerotic lesion severity and area (-33%), accompanied by a reduction in monocyte adhesion to the vessel wall (-42%) and macrophage content in the plaque (-44%). Furthermore, exendin-4 reduced hepatic lipid content and inflammation as well as hepatic CD68⁺ (-18%) and F4/80⁺ (-25%) macrophage content. This was accompanied by less monocyte recruitment from the circulation as the Mac-1⁺ macrophage content was decreased (-36%). Finally, exendin-4 reduced hepatic chemokine expression in vivo and suppressed oxidized low-density lipoprotein accumulation in peritoneal macrophages in vitro, effects dependent on the GLP-1 receptor.

CONCLUSIONS AND IMPLICATIONS

Exendin-4 reduces inflammation in both the liver and vessel wall by reducing macrophage recruitment and activation. These data suggest that exendin-4 could be a valuable strategy to treat NASH and atherosclerosis simultaneously.

Abstract 475: Circulating Immunoglobulins Are Not Associated With Intraplaque Mast Cell Number and Other Vulnerable Plaque Characteristics in Patients With Carotid Artery Stenosis

Background: Atherosclerosis is a chronic systemic inflammatory disease in which many immune cells participate. Recently we have shown that mast cell numbers are associated with atherosclerotic plaque vulnerability and interestingly with future cardiovascular events (S. Willems et.al. 2013). The endogenous trigger that activates mast cells within the lesion remains unidentified. We hypothesized that mast cells are activated via receptors for IgG and/or IgE.

In this study we aimed to establish whether specific immunoglobulin levels in plasma of atherosclerotic patients were related to intraplaque mast cell numbers. In addition, the levels were related to other vulnerable plaque characteristics and baseline clinical data.

Results: Serum levels of total IgG, total IgE and oxLDL specific IgG were determined in 135 patients that underwent carotid endarterectomy. The studied patient population with a mean age of 67 and a male prevalence (71%) reflects a relatively typical population of patients with vascular occlusive diseases. The majority of patients were symptomatic (74%) as illustrated by the incidence of amaurosis fugax, a TIA or a stroke.

No associations were observed between either the serum immunoglobulin levels or the total mast cell numbers in atherosclerotic plaques (total IgG vs. total mast cells r= -0,038, p=0.664) (tIgE vs total mast cells r=-0.038, p=0.664) (oxLDL-IgG vs total mast cells r=0.137 p=0.114). Furthermore, no associations were found between immunoglobulin levels and the following plaque characteristics: lipid core size, degree of calcification, number of macrophages or smooth muscle cells, amount of collagen and number of microvessels.

Interestingly, we observed a negative association between statin use and total IgE (97.5 [43.1-276.8] vs. 157.3 [75.2-545.4] ng/mL, p=0.012) and statin use and oxLDL-IgG (288 [224-406] vs. 399 [282-584] mU/mL, p=0.004).

Conclusions: In patients suffering from carotid artery disease, total IgG or IgE and oxLDL-IgG levels do not associate with plaque mast cell numbers or vulnerable plaque histopathological characteristics These data may indicate that other endogenous factors activate mast cells within the atherosclerotic plaque.

An unexpected intriguing effect of Toll-like receptor regulator RP105 (CD180) on atherosclerosis formation with alterations on B-cell activation

OBJECTIVE

In atherosclerosis, Toll-like receptors (TLRs) are traditionally linked to effects on tissue macrophages or foam cells. RP105, a structural TLR4 homolog, is an important regulator of TLR signaling. The effects of RP105 on TLR signaling vary for different leukocyte subsets known to be involved in atherosclerosis, making it unique in its role of either suppressing (in myeloid cells) or enhancing (in B cells) TLR-regulated inflammation in different cell types. We aimed to identify a role of TLR accessory molecule RP105 on circulating cells in atherosclerotic plaque formation.

APPROACH AND RESULTS

Irradiated low density lipoprotein receptor deficient mice received RP105(-/-) or wild-type bone marrow. RP105(-/-) chimeras displayed a 57% reduced plaque burden. Interestingly, total and activated B-cell numbers were significantly reduced in RP105(-/-) chimeras. Activation of B1 B cells was unaltered, suggesting that RP105 deficiency only affected inflammatory B2 B cells. IgM levels were unaltered, but anti-oxidized low-density lipoprotein and anti-malondialdehyde-modified low-density lipoprotein IgG2c antibody levels were significantly lower in RP105(-/-) chimeras, confirming effects on B2 B cells rather than B1 B cells. Moreover, B-cell activating factor expression was reduced in spleens of RP105(-/-) chimeras.

CONCLUSIONS

RP105 deficiency on circulating cells results in an intriguing unexpected TLR-associated mechanisms that decrease atherosclerotic lesion formation with alterations on proinflammatory B2 B cells.

Mast cells in atherosclerosis

The mast cell, a potent inflammatory cell type, is widely distributed over several tissues, but particularly prominent at the interface exposed to the environment to act in the first line of defense against pathogens. Upon activation mast cells release granules, which contain a large panel of mediators, including neutral proteases (e.g. chymase and tryptase), cathepsins, heparin, histamine and a variety of cytokines and growth factors. While mast cells have been demonstrated to be critically involved in a number of Th2 dominated diseases such as asthma and allergy, recent investigations have now also implicated mast cells in the pathogenesis of atherosclerosis and acute cardiovascular syndromes. In this review, we will discuss the contribution of mast cells to the initiation and progression of atherosclerosis and gauge the therapeutic opportunities of mast cell targeted intervention in acute cardiovascular syndromes.

Vaccination against Foxp3(+) regulatory T cells aggravates atherosclerosis

OBJECTIVE

Regulatory T cells are crucial for immune homeostasis and an impaired regulatory T cell function results in many pathological conditions. Regulatory T cells have already been described to be protective in atherosclerosis. However the exact contribution of Foxp3-expressing natural regulatory T cells in atherosclerosis has not been elucidated yet.

METHODS AND RESULTS

In this study we vaccinated LDL receptor deficient mice with dendritic cells which are transfected with Foxp3 encoding mRNA and studied the effect on initial atherosclerosis. Vaccination against Foxp3 resulted in a reduction of Foxp3(+) regulatory T cells in several organs and in an increase in initial atherosclerotic lesion formation. Furthermore we observed an increase in plaque cellularity and increased T cell proliferation in the Foxp3 vaccinated mice.

CONCLUSION

We further establish the protective role of Tregs in atherosclerosis. The results illustrate the important role for Foxp3-expressing regulatory T cells in atherosclerosis, thereby providing a potential opportunity for therapeutic intervention against this disease.

Leukocyte cathepsin S is a potent regulator of both cell and matrix turnover in advanced atherosclerosis

OBJECTIVE

A dysbalance of proteases and their inhibitors is instrumental in remodeling of atherosclerotic plaques. One of the proteases implicated in matrix degradation is cathepsin-S (CatS). To address its role in advanced lesion composition, we generated chimeric LDLr(-/-) mice deficient in leukocyte CatS by transplantation with CatS(-/-)xLDLr(-/-) or with LDLr(-/-) bone marrow and administered a high-fat diet.

METHODS AND RESULTS

No difference in aortic root lesion size could be detected between CatS(+/+) and CatS(-/-) chimeras. However, leukocyte CatS deficiency markedly changed plaque morphology and led to a dramatic reduction in necrotic core area by 77% and an abundance of large foam cells. Plaques of CatS(-/-) chimeras contained 17% more macrophages, 62% less SMCs, and 33% less intimal collagen. The latter two could be explained by a reduced number of elastic lamina fractures. Moreover, macrophage apoptosis was reduced by 60% with CatS deficiency. In vitro, CatS was found to be involved in cholesterol metabolism and in macrophage apoptosis in a collagen and fibronectin matrix.

CONCLUSIONS

Leukocyte CatS deficiency results in considerably altered plaque morphology, with smaller necrotic cores, reduced apoptosis, and decreased SMC content and collagen deposition and may thus be critical in plaque stability.

Identification of an Internalising Peptide in Differentiated Calu-3 Cells by Phage Display Technology; Application to Gene Delivery to the Airways

Differentiated, human submucosal-gland carcinoma, Calu-3 cell monolayers were used as in vitro model for the airway epithelium. Internalised phage were selected from a recombinant pComb8 phage library by repetitive cycles of bio-panning on Calu-3 monolayers, protease K degradation, cell-lysis and amplification. After four selection rounds, sequence analysis of 15 enriched phage colonies revealed two clones of 73 and 27% abundancy, named IB1 and IB2, respectively. The IB2 sequence was eliminated due to a frame shift. IB1-phage internalisation at 4 degrees C was significantly lower (P < 0.05) than at 37 degrees C, suggesting involvement of a receptor-mediated endocytosis pathway. The IB1 peptide was synthesised, biotinylated and complexed to streptavidin. IB1/streptavidin-complexes co-administrated with PEI/DNA-polyplexes, enhanced polyplex transfection efficiency, dose dependently, by 6- and 4-fold in Calu-3 cells. IB1/Alexa488-streptavidin complexes were used for confocal laser-scanning microscopy (CLSM) visualisation and showed basolateral localisation in membrane associated and internalising vesicles. This study demonstrates the potential of phage display technology for identification of internalising peptide-epitopes that can enhance gene delivery efficiency in differentiated airway epithelial cells.

Fibrin and Activated Platelets Cooperatively Guide Stem Cells to a Vascular Injury and Promote Differentiation Towards an Endothelial Cell Phenotype

Objective— Bone marrow-derived progenitor cells play a role in vascular regeneration. However, their homing to areas of vascular injury is poorly understood. One of the earliest responses to an injury is the activation of coagulation and platelets. In this study we assessed the role of hemostatic components in the recruitment of CD34 + cells to sites of injury.

Methods and Results— Using an ex vivo injury model, representing endothelial cell (EC) injury or vessel denudation, we studied homing of CD34 + under flow. Platelet aggregates facilitated initial tethering and rolling of CD34 + cells through interaction of P-selectin expressed by platelets and P-selectin glycoprotein ligand-1 (PSGL-1), expressed by CD34 + cells. Ligation of PSGL-1 activated adhesion molecules on CD34 + cells, ultimately leading to firm adhesion of CD34 + cells to tissue factor-expressing ECs or to fibrin-containing thrombi formed on subendothelium. We also demonstrate that fibrin-containing thrombi can support migration of CD34 + cells to the site of injury and subsequent differentiation toward a mature EC phenotype. Additionally, intravenously injected CD34 + cells homed in vivo to denuded arteries in the presence of endogenous leukocytes.

Conclusions— We provide evidence that hemostatic factors, associated with vascular injury, provide a regulatory microenvironment for re-endothelialization mediated by circulating progenitor cells.