Reduced Immunoregulatory CD31+T Cells in the Blood of Atherosclerotic Mice With Plaque Thrombosis

Mumefural Improves Blood Flow in a Rat Model of FeCl3-Induced Arterial Thrombosis

Mumefural (MF), a bioactive component of the processed fruit of Prunus mume Sieb. et Zucc, is known to inhibit platelet aggregation induced by agonists in vitro. In this study, we investigated the anti-thrombotic effects of MF using a rat model of FeCl₃-induced arterial thrombosis. Sprague–Dawley rats were intraperitoneally injected with MF (0.1, 1, or 10 mg/kg) 30 min before 35% FeCl₃ treatment to measure the time to occlusion using a laser Doppler flowmeter and to assess the weight of the blood vessels containing thrombus. MF treatment significantly improved blood flow by inhibiting occlusion and thrombus formation. MF also prevented collagen fiber damage in injured vessels and inhibited the expression of the platelet activation-related proteins P-selectin and E-selectin. Moreover, MF significantly reduced the increased inflammatory signal of nuclear factor (NF)-κB, toll-like receptor 4 (TLR4), tumor necrosis factor (TNF)-α, and interleukin (IL)-6 in blood vessels. After administration, MF was detected in the plasma samples of rats with a bioavailability of 36.95%. Therefore, we suggest that MF may improve blood flow as a candidate component in dietary supplements for improving blood flow and preventing blood circulation disorders.

CD31 as a Therapeutic Target in Atherosclerosis

The potential of CD31 as a therapeutic target in atherosclerosis has been considered ever since its cloning in the 1990s, but the exact role played by this molecule in the biologic events underlying atherosclerosis has remained controversial, resulting in the stalling of any therapeutic perspective. Due to the supposed cell adhesive properties of CD31, specific monoclonal antibodies and recombinant proteins were regarded as blocking agents because their use prevented the arrival of leukocytes at sites of acute inflammation. However, the observed effect of those compounds likely resulted from the engagement of the immunomodulatory function of CD31 signaling. This was acknowledged only later though, upon the discovery of CD31's 2 intracytoplasmic tyrosine residues called immunoreceptor tyrosine inhibitory motifs. A growing body of evidence currently points at a therapeutic potential for CD31 agonists in atherothrombosis. Clinical observations show that CD31 expression is altered at the surface of leukocytes infiltrating unhealed atherothrombotic lesions and that the physiological immunomodulatory functions of CD31 are lost at the surface of blood leukocytes in patients with acute coronary syndromes. On the contrary, translational studies using candidate therapeutic molecules in laboratory animals have provided encouraging results: synthetic peptides administered to atherosclerotic mice as systemic drugs in the acute phases of atherosclerotic complications favor the healing of wounded arteries, whereas the immobilization of CD31 agonist peptides onto coronary stents implanted in farm pigs favors their peaceful integration within the coronary arterial wall.

Cleaved CD31 as a target for in vivo molecular imaging of inflammation

There is a need for new targets to specifically localize inflammatory foci, usable in a wide range of organs. Here, we hypothesized that the cleaved molecular form of CD31 is a suitable target for molecular imaging of inflammation. We evaluated a bioconjugate of D-P8RI, a synthetic peptide that binds all cells with cleaved CD31, in an experimental rat model of sterile acute inflammation. Male Wistar rats were injected with turpentine oil into the gastrocnemius muscle two days before ^99mTc-HYNIC-D-P8RI (or its analogue with L-Proline) SPECT/CT or [¹⁸F]FDG PET/MRI. Biodistribution, stability study, histology, imaging and autoradiography of ^99mTc-HYNIC-D-P8RI were further performed. Biodistribution studies revealed rapid elimination of ^99mTc-HYNIC-D-P8RI through renal excretion with almost no uptake from most organs and excellent in vitro and in vivo stability were observed. SPECT/CT imaging showed a significant higher ^99mTc-HYNIC-D-P8RI uptake compared with its analogue with L-Proline (negative control) and no significant difference compared with [¹⁸F]FDG (positive control). Moreover, autoradiography and histology revealed a co-localization between ^99mTc-HYNIC-D-P8RI uptake and inflammatory cell infiltration. ^99mTc-HYNIC-D-P8RI constitutes a new tool for the detection and localization of inflammatory sites. Our work suggests that targeting cleaved CD31 is an attractive strategy for the specific in vivo imaging of inflammatory processes.

Matrix metalloproteinase-9 might affect adaptive immunity in non-ST segment elevation acute coronary syndromes by increasing CD31 cleavage on CD4+ T-cells

Aims

In patients with acute coronary syndrome (ACS), the higher activity of effector T-cells suggests that mechanisms involving adaptive immunity dysregulation might play a role in coronary instability. The shedding of the functional CD31 domain 1–5 leads to uncontrolled lymphocyte activation. In experimental models, matrix metalloproteinase-9 (MMP-9) has been implicated in endothelial CD31 cleavage. Interestingly, higher serum levels of MMP-9 have been observed in ACS. We aim to investigate the mechanisms underlying CD31 dysregulation in ACS.

Methods and results

To assess CD31 cleavage on CD4+ T-cells, we analysed by flow cytometry CD4+ T-cells of 30 ACS, 25 stable angina (SA) patients, and 28 controls (CTRL) using two different CD31 antibodies that specifically recognize domain 1–5 or the non-functional membrane-proximal domain 6. The ratio between the domains was significantly lower in ACS than in SA and CTRL (P = 0.002 ACS vs. SA; P = 0.002 ACS vs. CTRL). After stimulation with anti-CD3/CD28, the 1–5/6 domain ratio was significantly lower in ACS than in SA (P = 0.005). ELISA of supernatants obtained from T-cell receptor-stimulated CD4+ T-cells showed higher production of MMP-9 in ACS than in SA (P < 0.001). CD31 domain 1–5 expression in activated CD4+ T-cells from ACS patients increased after treatment with a specific MMP-9 inhibitor (P = 0.042).

Conclusion

Our study suggest that enhanced MMP-9 release plays a key role in determining the cleavage and shedding of the functional CD31 domain 1–5 in CD4+ T-cells of ACS patients. This mechanism might represent an important therapeutic target to modulate T-cell dysregulation in ACS.

Exercise and Cardiovascular Progenitor Cells

Autologous stem/progenitor cell-based methods to restore blood flow and function to ischemic tissues are clinically appealing for the substantial proportion of the population with cardiovascular diseases. Early preclinical and case studies established the therapeutic potential of autologous cell therapies for neovascularization in ischemic tissues. However, trials over the past ∼15 years reveal the benefits of such therapies to be much smaller than originally estimated and a definitive clinical benefit is yet to be established. Recently, there has been an emphasis on improving the number and function of cells [herein generally referred to as circulating angiogenic cells (CACs)] used for autologous cell therapies. CACs include of several subsets of circulating cells, including endothelial progenitor cells, with proangiogenic potential that is largely exerted through paracrine functions. As exercise is known to improve CV outcomes such as angiogenesis and endothelial function, much attention is being given to exercise to improve the number and function of CACs. Accordingly, there is a growing body of evidence that acute, short-term, and chronic exercise have beneficial effects on the number and function of different subsets of CACs. In particular, recent studies show that aerobic exercise training can increase the number of CACs in circulation and enhance the function of isolated CACs as assessed in ex vivo assays. This review summarizes the roles of different subsets of CACs and the effects of acute and chronic exercise on CAC number and function, with a focus on the number and paracrine function of circulating CD34+ cells, CD31+ cells, and CD62E+ cells. © 2019 American Physiological Society. Compr Physiol 9:767-797, 2019.

Effect of soluble cleavage products of important receptors/ligands on efferocytosis: Their role in inflammatory, autoimmune and cardiovascular disease

Efferocytosis, the clearance of apoptotic cells (ACs), is a physiologic, multifaceted and dynamic process and a fundamental mechanism for the preservation of tissue homeostasis by avoiding unwanted inflammation and autoimmune responses through special phagocytic receptors. Defective efferocytosis is associated with several disease states, including cardiovascular disease and impaired immune surveillance, as occurs in cancer and autoimmune disease. A major cause of defective efferocytosis is non-functionality of surface receptors on either the phagocytic cells or the ACs, such as TAM family tyrosine kinase, which turns to a soluble form by cleavage/shedding or alternative splicing. Recently, soluble forms have featured prominently as potential biomarkers, indicative of prognosis and enabling targeted therapy using several commonly employed drugs and inhibitors, such as bleomycin, dexamethasone, statins and some matrix metalloproteinase inhibitors such as TAPI-1 and BB3103. Importantly, to design drug carriers with enhanced circulatory durability, the adaptation of soluble forms of physiological receptors/ligands has been purported. Research has shown that soluble forms are more effective than antibody forms in enabling targeted treatment of certain conditions, such as autoimmune diseases. In this review, we sought to summarize the current knowledge of these soluble products, how they are generated, their interactions, roles, and their potential use as biomarkers in prognosis and treatment related to inflammatory, cardiovascular, and autoimmune diseases.

Metformin accelerates wound healing in type 2 diabetic db/db mice

Wound healing impairment is increasingly recognized to be a consequence of hyperglycemia-induced dysfunction of endothelial precursor cells (EPCs) in type 2 diabetes mellitus (T2DM). Metformin exhibits potential for the improvement of endothelial function and the wound healing process. However, the underlying mechanisms for the observed beneficial effects of metformin application remain to be completely understood. The present study assessed whether metformin, a widely used therapeutic drug for T2DM, may accelerate wound closure in T2DM db/db mice. Genetically hyperglycemic db/db mice were used as the T2DM model. Metformin (250 mg/kg/day; intragastric) was administered for two weeks prior to EPC collection and wound model creation in db/db mice. Wound healing was evaluated by alterations in the wound area and the number of platelet endothelial cell adhesion molecule-positive cells. The function of the isolated bone marrow-derived EPCs (BM-EPCs) was assessed by a tube formation assay. The number of circulating EPCs, and the levels of intracellular nitric oxide (NO) and superoxide (O₂⁻) were detected by flow cytometry. Thrombospondin-1 (TSP-1) expression was determined by western blot analysis. It was observed that treatment with metformin accelerated wound healing, improved angiogenesis and increased the circulating EPC number in db/db mice. In vitro, treatment with metformin reversed the impaired BM-EPC function reflected by tube formation, and significantly increased NO production while decreasing O₂⁻ levels in BM-EPCs from db/db mice. In addition, TSP-1 expression was markedly attenuated by treatment with metformin in cultured BM-EPCs. Metformin contributed to wound healing and improved angiogenesis in T2DM mice, which was, in part, associated with stimulation of NO, and inhibition of O₂⁻ and TSP-1 in EPCs from db/db mice.

CD31+ Cells From Peripheral Blood Facilitate Bone Regeneration in Biologically Impaired Conditions Through Combined Effects on Immunomodulation and Angiogenesis

Controlled revascularization and inflammation are key elements regulating endogenous regeneration after (bone) tissue trauma. Peripheral blood-derived cell subsets, such as regulatory T-helper cells and circulating (endothelial) progenitor cells, respectively, can support endogenous tissue healing, whereas effector T cells that are associated with an aged immune system can hinder bone regeneration. CD31 is expressed by diverse leukocytes and is well recognized as a marker of circulating endothelial (precursor) cells; however, CD31 is absent from the surface of differentiated effector T cells. Thus, we hypothesized that by separating the inhibitory fractions from the supportive fractions of circulating cells within the peripheral blood (PB) using the CD31 marker, bone regeneration in biologically compromised conditions, such as those observed in aged patients, could be improved. In support of our hypothesis, we detected an inverse correlation between CD31+ cells and effector T cells in the hematomas of human fracture patients, dependent on the age of the patient. Furthermore, we demonstrated the regenerative capacity of human PB-CD31+ cells in vitro. These findings were translated to a clinically relevant rat model of impaired bone healing. The transplantation of rat PB-CD31+ cells advanced bone tissue restoration in vivo and was associated with an early anti-inflammatory response, the stimulation of (re)vascularization, and reduced fibrosis. Interestingly, the depletion or enrichment of the highly abundant CD31+/14+ monocytes from the mixed CD31+ cell population diminished tissue regeneration at different levels, suggesting combined effects within the PB-CD31+ subsets. In summary, an intraoperative enrichment of PB-CD31+ cells might be a novel option to facilitate endogenous regeneration under biologically impaired situations by supporting immunomodulation and vascularization. © 2016 American Society for Bone and Mineral Research.

Decreased frequencies and impaired functions of the CD31+ subpopulation in Treg cells associated with decreased FoxP3 expression and enhanced Treg cell defects in patients with coronary heart disease

Coronary heart disease (CHD) is one of the most common types of organ lesions caused by atherosclerosis, in which CD4⁺ CD25⁺ forkhead box protein 3 (FoxP3⁺ ) regulatory T cells (T_reg ) play an atheroprotective role. However, T_reg cell numbers are decreased and their functions are impaired in atherosclerosis; the underlying mechanisms remain unclear. CD31 plays an important part in T cell response and contributes to maintaining T cell tolerance. The immunomodulatory effects of CD31 are also implicated in atherosclerosis. In this study, we found that decreased frequencies of the CD31⁺ subpopulation in T_reg cells (CD31⁺ Tr cells) correlated positively with decreased FoxP3 expression in CHD patients. Cell culture in vitro demonstrated CD31⁺ Tr cells maintaining stable FoxP3 expression after activation and exhibited enhanced proliferation and immunosuppression compared with the CD31^- subpopulation in T_reg cells (CD31^- Tr cells). We also confirmed impaired secretion of transforming growth factor (TGF)-β1 and interleukin (IL)-10 in CD31⁺ Tr cells of CHD patients. Further analysis revealed reduced phospho-SHP2 (associated with CD31 activation) and phospho-signal transducer and activator of transcription-5 (STAT-5) (associated with FoxP3 transcription) levels in CD31⁺ Tr cells of CHD patients, suggesting that decreased FoxP3 expression in CD31⁺ Tr cells might be because of attenuated SHP2 and STAT-5 activation. These data indicate that decreased frequencies and impaired functions of the CD31⁺ Tr subpopulation associated with decreased FoxP3 expression give rise, at least in part, to T_reg cell defects in CHD patients. Our findings emphasize the important role of the CD31⁺ Tr subpopulation in maintaining T_reg cell normal function and may provide a novel explanation for impaired immunoregulation of T_reg cells in CHD.

Adaptive Immunity Dysregulation in Acute Coronary Syndromes: From Cellular and Molecular Basis to Clinical Implications

Although the early outcome of acute coronary syndrome (ACS) has considerably improved in the last decade, cardiovascular diseases still represent the main cause of morbidity and mortality worldwide. This is mainly because recurrence of ACS eventually leads to the pandemics of heart failure and sudden cardiac death, thus calling for a reappraisal of the mechanisms responsible for coronary instability. This review discusses recent advances in our understanding of how adaptive immunity contributes to the pathogenesis of ACS and the clinical implications that arise from these new pathogenic concepts.

Reduced T-Cell Thymic Export Reflected by sj-TREC in Patients with Coronary Artery Disease

AIM

Immunologic dysfunction was recently found to be one of the most important mechanisms underlying the initiation and development of atherosclerosis. Thymus involution can contribute to immune disturbance and disequilibrium of T-cell subsets. This study aimed to explore whether recent thymic emigration (RTE) is impaired in patients with coronary artery disease (CAD).

METHODS

Content of signal-joint T cell receptor excision circles (sj-TREC) in T lymphocytes, a molecular marker of RTE, was assessed among CAD patients and age-matched controls. Monochrome multiplex quantitative PCR method was used to assess the samples' telomere length in order to exclude the potential influence of T cell proliferation on the dilution of sj-TREC. Patients were grouped according to Gensini score (GS) (low, GS ＜18; intermediate, GS 18-41; high, GS ＞41). Ordinary logistic regression models were used to determine potential risk factors for CAD and GS tertiles.

RESULTS

Average copy numbers of sj-TREC per 10(6) T lymphocytes among patients with unstable angina, stable angina, and controls were 726±429, 1213±465, and 1795±838, respectively (P＜0.001). However, there was no significant difference in telomere length among groups. Moreover, the content of sj-TREC in the high GS group was most significantly reduced than the low GS group (P＜0.001). Multivariate logistic regression analysis revealed that lower sj-TREC was independently associated with the progression of CAD (OR=0.44, P＜0.001) and higher GS (OR=0.4, P＜0.001).

CONCLUSION

Impaired RTE could be partly responsible for CAD development. Mechanisms may be involved in the disturbance of T lymphocyte compartment and interruption of maintained immune tolerance resulting from thymus involution.

CD31 signals confer immune privilege to the vascular endothelium

Constitutive resistance to cell death induced by inflammatory stimuli activating the extrinsic pathway of apoptosis is a key feature of vascular endothelial cells (ECs). Although this property is central to the maintenance of the endothelial barrier during inflammation, the molecular mechanisms of EC protection from cell-extrinsic, proapoptotic stimuli have not been investigated. We show that the Ig-family member CD31, which is expressed by endothelial but not epithelial cells, is necessary to prevent EC death induced by TNF-α and cytotoxic T lymphocytes in vitro. Combined quantitative RT-PCR array and biochemical analysis show that, upon the engagement of the TNF receptor with TNF-α on ECs, CD31 becomes activated and, in turn, counteracts the proapoptotic transcriptional program induced by TNF-α via activation of the Erk/Akt pathway. Specifically, Akt activation by CD31 signals prevents the localization of the forkhead transcription factor FoxO3 to the nucleus, thus inhibiting transcription of the proapoptotic genes CD95/Fas and caspase 7 and de-repressing the expression of the antiapoptotic gene cFlar. Both CD31 intracellular immunoreceptor tyrosine-based inhibition motifs are required for its prosurvival function. In vivo, CD31 gene transfer is sufficient to recapitulate the cytoprotective mechanisms in CD31(-) pancreatic β cells, which become resistant to immune-mediated rejection when grafted in fully allogeneic recipients.

Developmentally determined reduction in CD31 during gestation is associated with CD8+ T cell effector differentiation in preterm infants

Homeostatic T cell proliferation is more robust during human fetal development. In order to understand the relative effect of normal fetal homeostasis and perinatal exposures on CD8+ T cell behavior in PT infants, we characterized umbilical cord blood CD8+ T cells from infants born between 23-42weeks gestation. Subjects were recruited as part of the NHLBI-sponsored Prematurity and Respiratory Outcomes Program. Cord blood from PT infants had fewer naïve CD8+ T cells and lower regulatory CD31 expression on both naïve and effector, independent of prenatal exposures. CD8+ T cell in vitro effector function was greater at younger gestational ages, an effect that was exaggerated in infants with prior inflammatory exposures. These results suggest that CD8+ T cells earlier in gestation have loss of regulatory co-receptor CD31 and greater effector differentiation, which may place PT neonates at unique risk for CD8+ T cell-mediated inflammation and impaired T cell memory formation.

Altered CD31 expression and activity in helper T cells of acute coronary syndrome patients

In acute coronary syndrome (ACS), T cell abnormalities are associated to a worse outcome. Loss of inhibitory activity of CD31, an Ig-like adhesion molecule, on peripheral leukocytes has been found to enhance atherosclerosis in experimental models. In this study, we examined the expression of CD31 on T cells, and its role on TCR signaling in 35 patients with non-ST elevation ACS, in 35 patients with stable angina (SA), and in 35 controls. Furthermore, 10 ACS and 10 SA patients were re-analyzed at 1-year follow-up. Flow-cytometry analysis showed that in ACS patients, CD31 expression was reduced on total CD4(+) and CD4(+)CD28(null) (P < 0.001, ACS vs. SA), on naïve (P < 0.001, ACS vs. SA) and on central-memory and effector-memory CD4(+) T cells (P < 0.05, ACS vs. SA and controls). The immunomodulatory effect of CD31 on TCR signaling of CD4(+) and CD4(+)CD28(null) T cells, was lower in ACS than SA patients (P < 0.05, for both comparisons). At 1-year follow-up, CD31 expression and function increased in ACS becoming similar to that found in SA. CD31 recruitment in the immunological synapse was lower in ACS than controls (P = 0.012). Moreover, CD31 modulated MAPK signaling and reduced the expression of T bet and Rorγ-t, necessary for Th1 and Th17 differentiation. Finally, we studied TCR signaling in CD31(+) naïve and primed T cell subsets observing a different pattern of protein phosphorylation. A CD31-mediated regulatory pathway is enhanced in SA and temporarily downregulated in ACS. As CD31 modulates both T cell activation, by increasing the threshold for TCR stimulation, and T cell differentiation, it might represent a novel molecular target to treat T cell abnormalities in ACS.

Porphyromonas gingivalis infection reduces regulatory T cells in infected atherosclerosis patients

Increasing evidence has shown periodontal pathogen Porphyromonas gingivalis (P.gingivalis) infection contributes to atherosclerosis (AS) progression. P.gingivalis fimbriae act as an important virulence factor in AS. Regulatory T cells (Tregs) may play a crucial role in autoimmune response during this process. However, whether P.gingivalis infection is associated with Tregs dysregulation during AS is still unknown and the prevalence of different P.gingivalis FimA genotypes during this process is unclear. Here we analyzed the distribution of Tregs and in P.gingivalis-infected atherosclerotic patients to reveal the relationship between P.gingivalis infection and Tregs reduction/dysfunction and to elucidate their role in periodontitis-AS interaction. FimA genotype was also examined to determine the prevalence of fimbriae. Our results showed that P.gingivalis infection reduced Tregs in atherosclerotic patients compared with non-atherosclerotic patients and health controls. Concentration of TGF-β1, which plays an important role in the development of Tregs, also decreased in P.gingivalis infected patients. Furthermore, type II FimA seems to show higher prevalence than the other five detected types. The population of Tregs further decreased in patients with type II FimA compared with the other types. P.gingivlias FimA genotype II was the dominant type associated with decreased Treg population. These results indicate that P.gingivalis infection may be associated with Tregs dysregulation in AS; type II FimA may be a predominant genotype in this process.

An immunologist's guide to CD31 function in T-cells

Although it is expressed by all leukocytes, including T-, B-lymphocytes and dendritic cells, the immunoglobulin-like receptor CD31 is generally regarded by immunologists as a marker of endothelial cell lineage that lacks an established functional role in adaptive immunity. This perception has recently been challenged by studies that reveal a key role for this molecule in the regulation of T-cell homeostasis, effector function and trafficking. The complexity of the biological functions of CD31 results from the integration of its adhesive and signaling functions in both the immune and vascular systems. Signaling by means of CD31 is induced by homophilic engagement during the interactions of immune cells and is mediated by phosphatase recruitment or activation through immunoreceptor tyrosine inhibitory motifs (ITIMs) that are located in its cytoplasmic tail. Loss of CD31 function is associated with excessive immunoreactivity and susceptibility to cytotoxic killing. Here, we discuss recent findings that have brought to light a non-redundant, complex role for this molecule in the regulation of T-cell-mediated immune responses, with large impact on our understanding of immunity in health and disease.

Neutrophil-lymphocyte ratio as a predictor of major adverse cardiac events among diabetic population: a 4-year follow-up study

The neutrophil-lymphocyte ratio (NLR) is an inflammatory marker of major adverse cardiac events (MACEs) in both acute coronary syndromes and stable coronary artery disease. The use of NLR as a predictive tool for MACEs among diabetic patients has not been elucidated. An observational study included 338 diabetic patients followed at our clinic between 2007 and 2011. Patients were arranged into equal tertiles according to the 2007 NLR. The MACEs included acute myocardial infarction, coronary revascularization, and mortality. The lowest NLR tertile (NLR < 1.6) had fewer MACEs compared with the highest NLR tertile (NLR > 2.36; MACEs were 6 of 113 patients vs 24 of 112 patients, respectively; P < .0001). In a multivariate model, the adjusted hazard ratio of third NLR tertile compared with first NLR tertile was 2.8 (95% confidence interval 1.12-6.98, P = .027). The NLR is a significant independent predictor of MACEs in diabetic patients. Further studies with larger numbers are needed.

A CD31-derived peptide prevents angiotensin II-induced atherosclerosis progression and aneurysm formation

AIMS

The loss of the inhibitory receptor CD31 on peripheral T lymphocytes is associated with the incidence of atherosclerotic complications such as abdominal aortic aneurysms (AAA) in patients and plaque thrombosis in mice. However, we have recently discovered that a small fragment of extracellular CD31 remains expressed on the surface of the apparently 'CD31-negative' T-cells and that it is possible to restore the CD31-mediated T-cell inhibition in vivo by using a synthetic CD31-derived peptide. Here, we wanted to evaluate the therapeutic potential of the peptide in an experimental model of accelerated atherosclerosis and AAA formation.

METHODS AND RESULTS

The effect of the murine CD31-derived peptide (aa 551-574, 1.5 mg/kg/day, sc) was evaluated on the extent of atherosclerotic plaques and the incidence of AAA in 28-week-old apolipoprotein E knockout mice (male, n ≥ 8/group) submitted to chronic angiotensin II infusion. The therapeutic mechanisms of the peptide were assessed by evaluating its effect on immune cell functions in vivo and in vitro. The prevalence of angiotensin II-induced AAA correlated with the loss of extracellular CD31 on T-cells. CD31 peptide treatment reduced both aneurysm formation and plaque size (P < 0.05 vs. control). Protection was associated with reduced perivascular leucocyte infiltration and T-cell activation in vivo. Functional in vitro studies showed that the peptide is able to suppress both T-cell and macrophage activation.

CONCLUSION

CD31 peptides could represent a new class of drugs intended to prevent the inflammatory cell processes, such as those underlying progression of atherosclerosis and development of AAA.

Lymphocyte count was significantly associated with hyper-LDL cholesterolemia independently of high-sensitivity C-reactive protein in apparently healthy Japanese

The aim of this study was to investigate the association between leukocyte subtype counts and hyper-LDL cholesterolemia, hypertriglyceridemia, and hypo-HDL cholesterolemia. Logistic regressions using hyper-LDL cholesterolemia, hypertriglyceridemia, and hypo-HDL cholesterolemia as a dependent variable and total leukocyte, basophil, eosinophil, neutrophil, lymphocyte, and monocyte counts as an independent variable were calculated adjusting for age, body mass index (BMI), high-sensitivity C-reactive protein (hs-CRP), smoking, drinking, and physical activity in apparently healthy Japanese men (1,803) and women (1,150). The odds ratio (OR) of hyper-LDL cholesterolemia for total leukocyte, eosinophil, and lymphocyte counts, the OR of hypertriglyceridemia for total leukocyte, eosinophil, neutrophil, and lymphocyte counts, and the OR of hypo-HDL cholesterolemia for total leukocyte, neutrophil, and lymphocyte counts were significant in men, and the OR of hyper-LDL cholesterolemia, for lymphocyte count, and the OR of hypo-HDL cholesterolemia for eosinophil count were significant in women. Lymphocyte count was significantly associated with hyper-LDL cholesterolemia independently of hs-CRP in apparently healthy Japanese.

Human aging and CD31+ T-cell number, migration, apoptotic susceptibility, and telomere length

CD31(+) T cells, or so-called "angiogenic T cells," have been shown to demonstrate vasculoprotective and neovasculogenic qualities. The influence of age on CD31(+) T-cell number and function is unclear. We tested the hypothesis that circulating CD31(+) T-cell number and migratory capacity are reduced, apoptotic susceptibility is heightened, and telomere length is shortened with advancing age in adult humans. Thirty-six healthy, sedentary men were studied: 12 young (25 ± 1 yr), 12 middle aged (46 ± 1 yr), and 12 older (64 ± 2 yr). CD31(+) T cells were isolated from peripheral blood samples by magnetic-activated cell sorting. The number of circulating CD31(+) T cells (fluorescence-activated cell sorting analysis) was lower (P < 0.01) in older (24% of CD3(+) cells) compared with middle-aged (38% of CD3(+) cells) and young (40% of CD3(+) cells) men. Migration (Boyden chamber) to both VEGF and stromal cell-derived factor-1α was markedly blunted (P < 0.05) in cells harvested from middle-aged [306.1 ± 45 and 305.6 ± 46 arbitrary units (AU), respectively] and older (231 ± 65 and 235 ± 62 AU, respectively) compared with young (525 ± 60 and 570 ± 62 AU, respectively) men. CD31(+) T cells from middle-aged and older men demonstrated greater apoptotic susceptibility, as staurosporine-stimulated intracellular caspase-3 activation was ∼ 40% higher (P < 0.05) than young. There was a progressive age-related decline in CD31(+) T-cell telomere length (young: 10,706 ± 220 bp; middle-aged: 10,179 ± 251 bp; and older: 9,324 ± 192 bp). Numerical and functional impairments in this unique T-cell subpopulation may contribute to diminished angiogenic potential and greater cardiovascular risk with advancing age.

Platelet-endothelial cell adhesion molecule-1 gene polymorphism and its soluble level are associated with ischemic stroke

Inflammation, characterized by the recruitment and adhesion of circulating leukocytes by cellular adhesion molecules, plays an important role in the pathogenesis of atherosclerosis. Genetic analyses of platelet-endothelial cell adhesion molecule-1 (PECAM-1), a key adhesion molecule in the progression of atherosclerosis, have provided conflicting results regarding the role of variation within the PECAM-1 gene and risk for coronary heart disease. No studies have examined the association of this polymorphism with ischemic stroke. Therefore, we investigated that PECAM-1 gene polymorphism and its soluble level are associated with ischemic stroke in Chinese population. We analyzed single-nucleotide polymorphisms of PECAM-1 gene Leu125Val, Asn563Ser, and Gly670Arg in 265 patients with ischemic stroke and 280 age- and sex-matched controls, using polymerase chain reaction-restriction fragment length polymorphism and DNA sequencing method, while soluble PECAM-1 (sPECAM-1) levels were measured by enzyme-linked immunosorbent assay. There were significant differences in the genotype and allele frequencies of PECAM-1 gene Leu125Val polymorphism between the group of patients with ischemic stroke and the control group (p < 0.05). sPECAM-1 levels were increased in patients with ischemic stroke compared with controls (p < 0.01). Moreover, genotypes carrying the PECAM-1 125Val variant allele were associated with increased PECAM-1 levels compared to the homozygous wild-type genotype in patients with ischemic stroke. The Leu125Val polymorphism of PECAM-1 and its sPECAM-1 levels are associated with ischemic stroke in Chinese population. Our data suggest that the PECAM-1 gene may play a role in the development of ischemic stroke.

TCR stimulation drives cleavage and shedding of the ITIM receptor CD31

CD31 is a transmembrane molecule endowed with T cell regulatory functions owing to the presence of 2 immunotyrosine-based inhibitory motifs. For reasons not understood, CD31 is lost by a portion of circulating T lymphocytes, which appear prone to uncontrolled activation. In this study, we show that extracellular T cell CD31 comprising Ig-like domains 1 to 5 is cleaved and shed from the surface of human T cells upon activation via their TCR. The shed CD31 can be specifically detected as a soluble, truncated protein in human plasma. CD31 shedding results in the loss of its inhibitory function because the necessary cis-homo-oligomerization of the molecule, triggered by the trans-homophilic engagement of the distal Ig-like domain 1, cannot be established by CD31(shed) cells. However, we show that a juxta-membrane extracellular sequence, comprising part of the domain 6, remains expressed at the surface of CD31(shed) T cells. We also show that the immunosuppressive CD31 peptide aa 551-574 is highly homophilic and possibly acts by homo-oligomerizing with the truncated CD31 remaining after its cleavage and shedding. This peptide is able to sustain phosphorylation of the CD31 ITIM(686) and of SHP2 and to inhibit TCR-induced T cell activation. Finally, systemic administration of the peptide in BALB/c mice efficiently suppresses Ag-induced T cell-mediated immune responses in vivo. We conclude that the loss of T cell regulation caused by CD31 shedding driven by TCR stimulation can be rescued by molecular tools able to engage the truncated juxta-membrane extracellular molecule that remains exposed at the surface of CD31(shed) cells.

Site-specific effects of PECAM-1 on atherosclerosis in LDL receptor-deficient mice

OBJECTIVE

Atherosclerosis is a vascular disease that involves lesion formation at sites of disturbed flow under the influence of genetic and environmental factors. Endothelial expression of adhesion molecules that enable infiltration of immune cells is important for lesion development. Platelet/endothelial cell adhesion molecule-1 (PECAM-1; CD31) is an adhesion and signaling receptor expressed by many cells involved in atherosclerotic lesion development. PECAM-1 transduces signals required for proinflammatory adhesion molecule expression at atherosusceptible sites; thus, it is predicted to be proatherosclerotic. PECAM-1 also inhibits inflammatory responses, on which basis it is predicted to be atheroprotective.

METHODS AND RESULTS

We evaluated herein the effect of PECAM-1 deficiency on development of atherosclerosis in LDL receptor-deficient mice. We found that PECAM-1 has both proatherosclerotic and atheroprotective effects, but that the former dominate in the inner curvature of the aortic arch whereas the latter dominate in the aortic sinus, branching arteries, and descending aorta. Endothelial cell expression of PECAM-1 was sufficient for its atheroprotective effects in the aortic sinus but not in the descending aorta, where the atheroprotective effects of PECAM-1 also required its expression on bone marrow-derived cells.

CONCLUSIONS

We conclude that PECAM-1 influences initiation and progression of atherosclerosis both positively and negatively, and that it does so in a site-specific manner.

Identification of a novel role of T cells in postnatal vasculogenesis: characterization of endothelial progenitor cell colonies

BACKGROUND

The colony number of early endothelial progenitor cells (EPCs) has been used as a quantitative indicator of the number of EPCs in the blood or as a biological marker of cardiovascular diseases. In the present study, we found a subset of T cells that were localized at the center of the EPC colony and played a pivotal role in colony formation and differentiation of early EPCs.

METHODS AND RESULTS

We found that CD3+ CD31+ CXCR4+ T cells (referred to as angiogenic T cells in the present study) constituted the center of EPC colonies during cultures of human peripheral blood mononuclear cells. These angiogenic T cells were required for colony formation and differentiation of early EPCs. They secreted high levels of angiogenic cytokines such as vascular endothelial growth factor, interleukin-8, and matrix metalloproteinases. Angiogenic T cells showed superior angiogenic potential to the other subset of T cells in the experiments with regard to Matrigel tube formation, adhesion, transendothelial migration, and collagen invasion assay, mainly through the stromal cell-derived factor 1/CXCR-4 axis. Furthermore, angiogenic T cells enhanced endothelial cell proliferation and function. In vivo study showed that angiogenic T cells play an important role in the process of vessel formation. Clinical study showed that the level of angiogenic T cells in the peripheral blood was well correlated with EPC colony numbers and had inverse relationships with age and the number of risk factors for coronary artery disease.

CONCLUSIONS

These findings suggest that angiogenic T cells could be a potential therapeutic target for ischemic cardiovascular diseases.

Atheroprotective effect of CD31 receptor globulin through enrichment of circulating regulatory T-cells

OBJECTIVES

This study was designed to evaluate whether replacing CD31 (PECAM-1) signaling can restore the regulation of lymphocyte activation and improve experimental atherosclerosis.

BACKGROUND

Atherosclerosis, the principal cause of myocardial infarction and stroke, is due to the development of a pathogenic immune response within the vascular wall and is aggravated by the reduction of regulatory T-cells. CD31, a transmembrane adhesion molecule with inhibitory signaling functions, is physiologically expressed on blood and vascular resting cells but is lost in pathologic conditions associated with atherosclerosis.

METHODS

Replacement therapy with a CD31 receptor globulin (Rg) was delivered by in vivo gene transfer in 6-week-old apolipoprotein E knockout mice (n = 14 per group) every 5 weeks for 6 months. Control groups were treated with a truncated CD31Rg or with vehicle alone. At the end of the study, plaque size and morphology and blood T-cell compartment were analyzed in all mice.

RESULTS

Atherosclerotic lesions of CD31Rg-treated mice were smaller (p < 0.01) and showed less neovascularization and intraplaque hemorrhage (p < 0.05) compared with control subjects. Furthermore, circulating regulatory T-cells were increased in vivo (p < 0.01) and showed normal suppressive function on proliferation of conventional T-cells in vitro. Indeed, CD31Rg treatment led to blunted blood T-cell activation (p < 0.05) and reduced T-cell infiltration within plaques (p < 0.01).

CONCLUSIONS

Our data suggest that CD31 plays a key role in the regulation of the immune response linked to atherosclerosis. CD31-targeting therapeutic approaches may therefore be envisaged for preventing and treating atherosclerotic diseases.

The opposite-direction modulation of CD4+CD25+ Tregs and T helper 1 cells in acute coronary syndromes

Different subsets of T lymphocytes have different functions in atherosclerosis advancement. T helper 1 cells and T regulatory 1 cells have been demonstrated to play opposite roles in rupture of atherosclerotic lesion. However, the role of novel subset of T regulatory cells, known as CD4+CD25+Foxp3+ T cells, remains largely unknown in coronary artery disease (CAD). In this study, we investigated the peripheral CD4+CD25+Foxp3+ T cells of patients with CAD and controls. The patients submitted were divided into three groups: stable angina pectoris (SA) group, unstable angina pectoris (UA) group and acute myocardial infarction (AMI) group. We analyzed the frequencies of peripheral CD4+CD25+Foxp3+ T cells and T helper 1/T helper 2 cells, expression of Foxp3 in CD4+CD25+ T subsets and cytokines pattern in patients and controls. We found that the reduction of CD4+CD25+Foxp3+ T lymphocytes was consistent with the expansion of Th1 cells in patients with unstable CAD. The reversed development between CD4+CD25+ Tregs and Th1 cells might contribute to plaque destabilization.

Association of peripheral total and differential leukocyte counts with metabolic syndrome and risk of ischemic cardiovascular diseases in patients with type 2 diabetes mellitus

BACKGROUND

There is increasing evidence that leukocytes play a central role in obesity, glucose intolerance, type 2 diabetes mellitus (T2DM), and cardiovascular diseases, but the role of differential leukocytes in metabolic syndrome (MetS) and atherosclerosis is largely unknown. The aim of this study was to examine the relationship between the component features of MetS and peripheral leukocyte counts and to explore whether leukocyte counts are associated with clustering of MetS and macrovascular diseases in patients with T2DM.

METHODS

1872 subjects with T2DM who enrolled in a diabetes disease management program were studied. The definition of MetS was modified from that outlined by the criteria of NCEP-ATP III. Areas under the receiver-operating characteristic curve and odds ratios at various intervals of the WBC counts were computed.

RESULTS

The peripheral total leukocyte, monocyte, and neutrophil cell counts are increased parallel to the clustering of components of MetS. When white cell counts were analyzed per quartile and as continuous variables after adjustment for age, sex, and other known risk factors with multiple regression analysis, peripheral total leukocyte, monocyte, neutrophils, and lymphocyte counts were independently and significantly associated with specific features of clustering of MetS and prevalence of ischemic cardiovascular diseases. Leukocyte counts, especially neutrophil/lymphocyte ratio, in addition with MetS is associated with the risk of ischemic cardiovascular diseases.

CONCLUSION

Our results indicate that differential leukocyte counts are associated with MetS and that peripheral leukocytes may play a role in the pathogenesis of macrovascular complications in patients with T2DM.

T cells in atherogenesis: for better or for worse?

The idea that atherosclerosis is an inflammatory disease is no longer controversial. Instead, much of the current research is now focused on understanding what drives this inflammation and how it is regulated. Adaptive immunity, in particular T cells, is highly involved in atherogenesis. It is well known that different subsets of T cells can drive or dampen inflammatory processes, but we still have much to learn about the regulation of this balance in the context of atherosclerosis. This review summarizes our knowledge of T cells in atherogenesis, their potential antigens, their contact-dependent activities, and their secretion of inflammatory and antiinflammatory mediators, aiming to illustrate how T cells can aggravate or attenuate this disease through cross-talk with other cells within or outside the atherosclerotic plaque.

Reduced Immunoregulatory CD31 + T Cells in Patients With Atherosclerotic Abdominal Aortic Aneurysm

Background— Cell-mediated immunity is considered to contribute to the pathogenesis of abdominal aortic aneurysms (AAA). In particular, infiltrating macrophages and CD8 + T lymphocytes participate in the destruction of the aortic wall extracellular matrix and smooth muscle cells. We surmise that these pathological events are controlled by circulating regulatory lymphocytes.

Methods and Results— Circulating CD4 + /CD31 + cells were reduced in AAA patients (n=80, 8.9±0.6%) as compared with controls (n=69, 13.7±0.8%; P <0.001) and inversely proportional to AAA size. Exclusion of the aneurysm by an endoprothesis did not affect CD31 + T cell values. Reduction of blood CD4 + /CD31 + cells was not attributable to their enrichment in AAA tissue. In contrast, CD8 + /CD31 + cells were slightly reduced in the blood while increased in the aneurysmal tissue (29.2±0.5 versus 20.2±4.7% in blood, n=6; P <0.05). Remarkably, high percentages of CD4 + /CD31 + cells were able to regulate proliferation and cytokine production of CD8 + lymphocytes, as well as CD8 + cell-mediated cytotoxicity of aortic smooth muscle cells ( P <0.01). Finally, CD4 + /CD31 + cells reduced the production and activity of metalloproteinase-9 by lipopolysaccharide-stimulated macrophages.

Conclusions— Circulating CD4 + /CD31 + T cells regulate macrophage and CD8 + T cell activation and effector function in the arterial wall. Their reduction might promote the development of AAA.