Resident and recruited macrophages differentially contribute to cardiac healing after myocardial ischemia.

Cardiac macrophages are heterogenous in phenotype and functions, which has been associated with differences in their ontogeny. Despite extensive research, our understanding of the precise role of different subsets of macrophages in ischemia/reperfusion (I/R) injury remains incomplete. We here investigated macrophage lineages and ablated tissue macrophages in homeostasis and after I/R injury in a CSF1R-dependent manner. Genomic deletion of a fms-intronic regulatory element (FIRE) in the Csf1r locus resulted in specific absence of resident homeostatic and antigen-presenting macrophages, without affecting the recruitment of monocyte-derived macrophages to the infarcted heart. Specific absence of homeostatic, monocyte-independent macrophages altered the immune cell crosstalk in response to injury and induced proinflammatory neutrophil polarization, resulting in impaired cardiac remodeling without influencing infarct size. In contrast, continuous CSF1R inhibition led to depletion of both resident and recruited macrophage populations. This augmented adverse remodeling after I/R and led to an increased infarct size and deterioration of cardiac function. In summary, resident macrophages orchestrate inflammatory responses improving cardiac remodeling, while recruited macrophages determine infarct size after I/R injury. These findings attribute distinct beneficial effects to different macrophage populations in the context of myocardial infarction.

Myeloperoxidase induces monocyte migration and activation after acute myocardial infarction.

Introduction: Myocardial infarction (MI) is a significant contributor to morbidity and mortality worldwide. Many individuals who survive the acute event continue to experience heart failure (HF), with inflammatory and healing processes post-MI playing a pivotal role. Polymorphonuclear neutrophils (PMN) and monocytes infiltrate the infarcted area, where PMN release high amounts of the heme enzyme myeloperoxidase (MPO). MPO has numerous inflammatory properties and MPO plasma levels are correlated with prognosis and severity of MI. While studies have focused on MPO inhibition and controlling PMN infiltration into the infarcted tissue, less is known on MPO's role in monocyte function. Methods and results: Here, we combined human data with mouse and cell studies to examine the role of MPO on monocyte activation and migration. We revealed a correlation between plasma MPO levels and monocyte activation in a patient study. Using a mouse model of MI, we demonstrated that MPO deficiency led to an increase in splenic monocytes and a decrease in cardiac monocytes compared to wildtype mice (WT). In vitro studies further showed that MPO induces monocyte migration, with upregulation of the chemokine receptor CCR2 and upregulation of inflammatory pathways identified as underlying mechanisms. Conclusion: Taken together, we identify MPO as a pro-inflammatory mediator of splenic monocyte recruitment and activation post-MI and provide mechanistic insight for novel therapeutic strategies after ischemic injury.

The novel vaccines targeting interleukin-1 receptor type I.

OBJECTIVE: There is mounting evidence indicating that atherosclerosis represents a persistent inflammatory process, characterized by the presence of inflammation at various stages of the disease. Interleukin-1 (IL-1) precisely triggers inflammatory signaling pathways by binding to interleukin-1 receptor type I (IL-1R1). Inhibition of this signaling pathway contributes to the prevention of atherosclerosis and myocardial infarction. The objective of this research is to develop therapeutic vaccines targeting IL-1R1 as a preventive measure against atherosclerosis and myocardial infarction. METHODS: ILRQß-007 and ILRQß-008 vaccines were screened, prepared and then used to immunize high-fat-diet fed ApoE-/- mice and C57BL/6J mice following myocardial infarction. Progression of atherosclerosis in ApoE-/- mice was assessed primarily by oil-red staining of the entire aorta and aortic root, as well as by detecting the extent of macrophage infiltration. The post-infarction cardiac function in C57BL/6J mice were evaluated using cardiac ultrasound and histological staining. RESULTS: ILRQß-007 and ILRQß-008 vaccines stimulated animals to produce high titers of antibodies that effectively inhibited the binding of interleukin-1ß and interleukin-1α to IL-1R1. Both vaccines effectively reduced atherosclerotic plaque area, promoted plaque stabilization, decreased macrophage infiltration in plaques and influenced macrophage polarization, as well as decreasing levels of inflammatory factors in the aorta, serum, and ependymal fat in ApoE-/- mice. Furthermore, these vaccines dramatically improved cardiac function and macrophage infiltration in C57BL/6J mice following myocardial infarction. Notably, no significant immune-mediated damage was observed in immunized animals. CONCLUSION: The vaccines targeting the IL-1R1 would be a novel and promising treatment for the atherosclerosis and myocardial infarction.

Regulatory T-cell frequency and function in acute myocardial infarction patients and its correlation with ventricular dysfunction.

A high percentage of patients with acute coronary syndrome develop heart failure due to the ischemic event. Regulatory T (Treg) cells are lymphocytes with suppressive capacity that control the immune response and include the conventional CD4+ CD25hi Foxp3+ cells and the CD4+ CD25var CD69+ LAP+ Foxp3- IL-10+ cells. No human follow-up studies focus on Treg cells' behavior after infarction and their possible relationship with ventricular function as a sign of postischemic cardiac remodeling. This study aimed to analyze, by flow cytometry, the circulating levels of CD69+ Treg cells and CD4+ CD25hi Foxp3+ cells, their IL-10+ production as well as their function in patients with acute myocardial infarction (AMI), and its possible relation with ventricular dysfunction. We found a significant difference in the percentage of CD4+ CD25hi Foxp3+ cells and IL-10+ MFI in patients with AMI at 72 hours compared with the healthy control group, and the levels of these cells were reduced 6 months post-AMI. Regarding the suppressive function of CD4+ CD25+ regulatory cells, they were dysfunctional at 3 and 6 months post-AMI. The frequency of CD69+ Treg cells was similar between patients with AMI at 72 hours postinfarction and the control groups. Moreover, the frequency of CD69+ Treg cells at 3 and 6 months postischemic event did not vary over time. Treg cells play a role in regulating inflammation after an AMI, and its function may be compromised in this pathology. This work is the first report to evaluate CD69+ Foxp3- Treg cells in AMI patients.

Microglia-Mediated Neuroimmune Response Regulates Cardiac Remodeling After Myocardial Infarction.

Background Sympathetic hyperactivity contributes to pathological remodeling after myocardial infarction (MI). However, the mechanisms underlying the increase in sympathetic activity remain unknown. Microglia are the predominant immune cells in the central nervous system and can regulate sympathetic neuron activity through neuroimmune response in the hypothalamic paraventricular nucleus. The present study aimed to investigate whether microglia-mediated neuroimmune response can regulate sympathetic activity and cardiac remodeling after MI. Methods and Results PLX3397 (pexidartinib) was used to deplete central microglia via intragastric injection or intracerebroventricular injection. After that, MI was induced by ligation of the left anterior descending coronary artery. Our study showed that MI resulted in the activation of microglia in the paraventricular nucleus. Microglia depletion, which was induced by PLX3397 treatment via intragastric injection or intracerebroventricular injection, improved cardiac function, reduced infarction size, and attenuated cardiomyocyte apoptosis, fibrosis, pathological electrical remodeling, and myocardial inflammation after MI. Mechanistically, these protective effects were associated with an attenuated neuroimmune response in the paraventricular nucleus, which contributed to the decrease of sympathetic activity and attenuation of sympathetic remodeling in the heart. However, intragastric injection with PLX3397 obviously depleted macrophages and induced neutrophil and T-lymphocyte disorders in the heart, blood, and spleen. Conclusions Microglia depletion in the central nervous system attenuates pathological cardiac remodeling after MI by inhibiting neuroimmune response and sympathetic activity. Intragastric administration of PLX3397 leads to serious deleterious effects in peripheral immune cells, especially macrophages, which should be a cause for concern in animal experiments and clinical practice.

Single-Cell Sequencing Revealed Pivotal Genes Related to Prognosis of Myocardial Infarction Patients.

Objectives: Myocardial infarction (MI) is a common cardiovascular disease. Histopathology is a main molecular characteristic of MI, but often, differences between various cell subsets have been neglected. Under this premise, MI-related molecular biomarkers were screened using single-cell sequencing. Methods: This work examined immune cell abundance in normal and MI samples from GSE109048 and determined differences in the activated mast cells and activated CD4 memory T cells, resting mast cells. Weighted gene coexpression network analysis (WGCNA) demonstrated that activated CD4 memory T cells were the most closely related to the turquoise module, and 10 hub genes were screened. Single-cell sequencing data (scRNA-seq) of MI were examined. We used t-distributed stochastic neighbor embedding (t-SNE) for cell clustering. Results: We obtained 8 cell subpopulations, each of which had different marker genes. 7 out of the 10 hub genes were detected by single-cell sequencing analysis. The expression quantity and proportion of the 7 genes were different in 8 cell clusters. Conclusion: In general, our study revealed the immune characteristics and determined 7 prognostic markers for MI at the single-cell level, providing a new understanding of the molecular characteristics and mechanism of MI.

Selectin-targeting glycosaminoglycan-peptide conjugate limits neutrophil-mediated cardiac reperfusion injury.

AIMS: One of the hallmarks of myocardial infarction (MI) is excessive inflammation. During an inflammatory insult, damaged endothelial cells shed their glycocalyx, a carbohydrate-rich layer on the cell surface which provides a regulatory interface to immune cell adhesion. Selectin-mediated neutrophilia occurs as a result of endothelial injury and inflammation. We recently designed a novel selectin-targeting glycocalyx mimetic (termed DS-IkL) capable of binding inflamed endothelial cells. This study examines the capacity of DS-IkL to limit neutrophil binding and platelet activation on inflamed endothelial cells, as well as the cardioprotective effects of DS-IkL after acute myocardial infarction. METHODS AND RESULTS: In vitro, DS-IkL diminished neutrophil interactions with both recombinant selectin and inflamed endothelial cells, and limited platelet activation on inflamed endothelial cells. Our data demonstrated that DS-IkL localized to regions of vascular inflammation in vivo after 45 min of left anterior descending coronary artery ligation-induced MI. Further, findings from this study show DS-IkL treatment had short- and long-term cardioprotective effects after ischaemia/reperfusion of the left anterior descending coronary artery. Mice treated with DS-IkL immediately after ischaemia/reperfusion and 24 h later exhibited reduced neutrophil extravasation, macrophage accumulation, fibroblast and endothelial cell proliferation, and fibrosis compared to saline controls. CONCLUSIONS: Our findings suggest that DS-IkL has great therapeutic potential after MI by limiting reperfusion injury induced by the immune response.

Augmented early aged neutrophil infiltration contributes to late remodeling post myocardial infarction.

Neutrophils oscillate in number and phenotype after being released from bone marrow. Myocardial infarction (MI) outcome is associated with the time-of-day of ischemia onset. However, the underlying contributive factors of neutrophils to cardiac remodeling post MI remain unknown. We examined neutrophil infiltration into the heart and cardiac function and remodeling in C57BL/6J MI model created by permanent coronary ligation at different zeitgeber times (ZT). We found that cell surface markers (CD62L, CXCR2, CXCR4) of neutrophils in peripheral blood lost diurnal oscillation 24 h post MI. Meanwhile, circadian gene Bmal1, Nr1d1, and Clock mRNA expression displayed disrupted diurnal patterns. Flow cytometry showed augmented aged neutrophil (CD11b+Ly6G+CD62Llow) infiltration into the heart along with increased circulating aged neutrophils in MI groups with more infiltration at ZT5 (p < 0.05), but no difference for aged neutrophil infiltration at different ZT points in late stage. Infiltrated neutrophils had significantly higher CXCL2 and CXCR2 but lower CXCR4 gene expression (p < 0.05). Mice that underwent ligation at ZT5 had high mortality rate and large infarct size. Echocardiography showed that those mice had significantly larger end diastolic and systolic volume and lower ejection fraction (p < 0.05). Immunohistology revealed that those mice displayed more fibrosis, cardiomyocyte hypertrophy, and less angiogenesis compared to ZT13 or ZT21 group (p < 0.05). However, treatment with anti-CXCL2 antibody significantly reduced LV dilatation, fibrosis, hypertrophy and improved cardiac function. These results indicate greater aged neutrophil infiltration into the heart contributes to cardiac hypertrophy, fibrosis, and dysfunction which suggests that blocking neutrophil aging may be a therapeutic alternative following acute myocardial infarction.

Cerebral derailment after myocardial infarct: mechanisms and effects of the signaling from the ischemic heart to brain.

Myocardial infarction (MI) is the leading cause of death among ischemic heart diseases and is associated with several long-term cardiovascular complications, such as angina, re-infarction, arrhythmias, and heart failure. However, MI is frequently accompanied by non-cardiovascular multiple comorbidities, including brain disorders such as stroke, anxiety, depression, and cognitive impairment. Accumulating experimental and clinical evidence suggests a causal relationship between MI and stroke, but the precise underlying mechanisms have not yet been elucidated. Indeed, the risk of stroke remains a current challenge in patients with MI, in spite of the improvement of medical treatment among this patient population has reduced the risk of stroke. In this review, the effects of the signaling from the ischemic heart to the brain, such as neuroinflammation, neuronal apoptosis, and neurogenesis, and the possible actors mediating these effects, such as systemic inflammation, immunoresponse, extracellular vesicles, and microRNAs, are discussed.

G protein-coupled receptor kinase 5 (GRK5) contributes to impaired cardiac function and immune cell recruitment in post-ischemic heart failure.

AIMS: Myocardial infarction (MI) is the most common cause of heart failure (HF) worldwide. G protein-coupled receptor kinase 5 (GRK5) is upregulated in failing human myocardium and promotes maladaptive cardiac hypertrophy in animal models. However, the role of GRK5 in ischemic heart disease is still unknown. In this study, we evaluated whether myocardial GRK5 plays a critical role post-MI in mice and included the examination of specific cardiac immune and inflammatory responses. METHODS AND RESULTS: Cardiomyocyte-specific GRK5 overexpressing transgenic mice (TgGRK5) and non-transgenic littermate control (NLC) mice as well as cardiomyocyte-specific GRK5 knockout mice (GRK5cKO) and wild type (WT) were subjected to MI and, functional as well as structural changes together with outcomes were studied. TgGRK5 post-MI mice showed decreased cardiac function, augmented left ventricular dimension and decreased survival rate compared to NLC post-MI mice. Cardiac hypertrophy and fibrosis as well as fetal gene expression were increased post-MI in TgGRK5 compared to NLC mice. In TgGRK5 mice, GRK5 elevation produced immuno-regulators that contributed to the elevated and long-lasting leukocyte recruitment into the injured heart and ultimately to chronic cardiac inflammation. We found an increased presence of pro-inflammatory neutrophils and macrophages as well as neutrophils, macrophages and T-lymphocytes at 4-days and 8-weeks respectively post-MI in TgGRK5 hearts. Conversely, GRK5cKO mice were protected from ischemic injury and showed reduced early immune cell recruitment (predominantly monocytes) to the heart, improved contractility and reduced mortality compared to WT post-MI mice. Interestingly, cardiomyocyte-specific GRK2 transgenic mice did not share the same phenotype of TgGRK5 mice and did not have increased cardiac leukocyte migration and cytokine or chemokine production post-MI. CONCLUSIONS: Our study shows that myocyte GRK5 has a crucial and GRK-selective role on the regulation of leucocyte infiltration into the heart, cardiac function and survival in a murine model of post-ischemic HF, supporting GRK5 inhibition as a therapeutic target for HF.

Innate Lymphoid Cells and Myocardial Infarction.

Myocardial infarction results from obstruction of a coronary artery that causes insufficient blood supply to the myocardium and leads to ischemic necrosis. It is one of the most common diseases threatening human health and is characterized by high morbidity and mortality. Atherosclerosis is the pathological basis of myocardial infarction, and its pathogenesis has not been fully elucidated. Innate lymphoid cells (ILCs) are an important part of the human immune system and participate in many processes, including inflammation, metabolism and tissue remodeling, and play an important role in atherosclerosis. However, their specific roles in myocardial infarction are unclear. This review describes the current understanding of the relationship between innate lymphoid cells and myocardial infarction during the acute phase of myocardial infarction, myocardial ischemia-reperfusion injury, and heart repair and regeneration following myocardial infarction. We suggest that this review may provide new potential intervention targets and ideas for treatment and prevention of myocardial infarction.

Identification of Biomarkers Related to Immune Cell Infiltration with Gene Coexpression Network in Myocardial Infarction.

BACKGROUND: There is evidence that the immune system plays a key critical role in the pathogenesis of myocardial infarction (MI). However, the exact mechanisms associated with immunity have not been systematically uncovered. METHODS: This study used the weighted gene coexpression network analysis (WGCNA) and the CIBERSORT algorithm to analyze the MI expression data from the Gene Expression Omnibus database and then identify the module associated with immune cell infiltration. In addition, we built the coexpression network and protein-protein interactions network analysis to identify the hub genes. Furthermore, the relationship between hub genes and NK cell resting was validated by using another dataset GSE123342. Finally, receiver operating characteristic (ROC) curve analyses were used to assess the diagnostic value of verified hub genes. RESULTS: Monocytes and neutrophils were markedly increased, and T cell CD8, T cell CD4 naive, T cell CD4 memory resting, and NK cell resting were significantly decreased in MI groups compared with stable coronary artery disease (CAD) groups. The WGCNA results showed that the pink model had the highest correlation with the NK cell resting infiltration level. We identified 11 hub genes whose expression correlated to the NK cell resting infiltration level, among which, 7 hub genes (NKG7, TBX21, PRF1, CD247, KLRD1, FASLG, and EOMES) were successfully validated in GSE123342. And these 7 genes had diagnostic value to distinguish MI and stable CAD. CONCLUSIONS: NKG7, TBX21, PRF1, CD247, KLRD1, FASLG, and EOMES may be a diagnostic biomarker and therapeutic target associated with NK cell resting infiltration in MI.

Difference of immune cell infiltration between stable and unstable carotid artery atherosclerosis.

Atherosclerotic plaque instability contributes to ischaemic stroke and myocardial infarction. This study is to compare the abundance and difference of immune cell subtypes within unstable atherosclerotic tissues. CIBERSORT was used to speculate the proportions of 22 immune cell types based on a microarray of atherosclerotic carotid artery samples. R software was utilized to illustrate the bar plot, heat map and vioplot. The immune cell landscape in atherosclerosis was diverse, dominated by M2 macrophages, M0 macrophages, resting CD4 memory T cells and CD8 T cells. There was a significant difference in resting CD4 memory T cells (p = 0.032), T cells follicular helper (p = 0.033), M0 (p = 0.047) and M2 macrophages (p = 0.012) between stable and unstable atherosclerotic plaques. Compared with stable atherosclerotic plaques, unstable atherosclerotic plaques had a higher percentage of M2 macrophages. Moreover, correlation analysis indicated that the percentage of naïve CD4 T cells was strongly correlated with that of gamma delta T cells (r = 0.93, p < 0.001), while memory B cells were correlated with plasma cells (r = 0.85, p < 0.001). In summary, our study explored the abundance and difference of specific immune cell subgroups at unstable plaques, which would aid new immunotherapies for atherosclerosis.

Chronic Porphyromonas gingivalis lipopolysaccharide induces adverse myocardial infarction wound healing through activation of CD8+ T cells.

Oral and gum health have long been associated with incidence and outcomes of cardiovascular disease. Periodontal disease increases myocardial infarction (MI) mortality by sevenfold through mechanisms that are not fully understood. The goal of this study was to evaluate whether lipopolysaccharide (LPS) from a periodontal pathogen accelerates inflammation after MI through memory T-cell activation. We compared four groups [no MI, chronic LPS, day 1 after MI, and day 1 after MI with chronic LPS (LPS + MI); n = 68 mice] using the mouse heart attack research tool 1.0 database and tissue bank coupled with new analyses and experiments. LPS + MI increased total CD8+ T cells in the left ventricle versus the other groups (P < 0.05 vs. all). Memory CD8+ T cells (CD44 + CD27+) were 10-fold greater in LPS + MI than in MI alone (P = 0.02). Interleukin (IL)-4 stimulated splenic CD8+ T cells away from an effector phenotype and toward a memory phenotype, inducing secretion of factors associated with the Wnt/ß-catenin signaling that promoted monocyte migration and decreased viability. To dissect the effect of CD8+ T cells after MI, we administered a major histocompatibility complex-I-blocking antibody starting 7 days before MI, which prevented effector CD8+ T-cell activation without affecting the memory response. The reduction in effector cells diminished infarct wall thinning but had no effect on macrophage numbers or MertK expression. LPS + MI + IgG attenuated macrophages within the infarct without effecting CD8+ T cells, suggesting these two processes were independent. Overall, our data indicate that effector and memory CD8+ T cells at post-MI day 1 are amplified by chronic LPS to potentially promote infarct wall thinning.NEW & NOTEWORTHY Although there is a well-documented link between periodontal disease and heart health, the mechanisms are unclear. Our study indicates that in response to circulating periodontal endotoxins, memory CD8+ T cells are activated, resulting in an acceleration of macrophage-mediated inflammation after MI. Blocking activation of effector CD8+ T cells had no effect on the macrophage numbers or wall thinning at post-MI day 1, indicating that this response was likely due in part to memory CD8+ T cells.

Down-regulation of VCAM-1 in bone mesenchymal stem cells reduces inflammatory responses and apoptosis to improve cardiac function in rat with myocardial infarction.

BACKGROUND: Bone mesenchymal stem cells (BMSCs) has been well known to exert therapeutic potential for patients with myocardial infarction (MI). VCAM-1 can promote the migration of lymphocytes to the inflammatory zone. In the present study, we tried to explore whether VCAM-1 silenced-BMSCs have better therapeutic effects on MI. METHODS: BMSCs were isolated and cultured followed by treatment of a lentivirus silencing VCAM-1 and NF-κB activator (PMA). Besides, MI rat models were also established and injected with treated BMSCs to detect the effect of VCAM-1 silenced-BMSCs in MI, as evidenced by detection of cardiac function, survival of rats within 72 h, infarct size and myocardial cell apoptosis. Moreover, the expression of NF-κB-regulated gene products was also determined. RESULTS: The implantation of sh-VCAM-1 BMSCs into MI rats resulted in more reductions in myocardial infarct size as well as myocardial cell apoptosis, improved cardiac function, the number of survived rats within 72 h, and survival time within 72 h compared with the individual treatments of either BMSCs or control. In addition, transplanted BMSCs down-regulated the expression of NF-κB-p65, MMP-9, TNF-α, and Bax, and up-regulated VEGF and Bcl-2 in myocardial tissue, which could be further enhanced by sh-VCAM-1 and rescued by PMA. CONCLUSION: Our study demonstrated that silencing VCAM-1 in BMSCs could inhibit inflammation and apoptosis, thus improving cardiac function in MI.

Fibroblast growth factor 21 inhibited inflammation and fibrosis after myocardial infarction via EGR1.

Myocardial fibrosis in post-myocardial infarction is a self-healing process of the myocardium, making ventricular remodelling difficult to reverse and develop continuously. Fibroblast growth factor 21 (FGF21) plays an essential role in cardiovascular and metabolic diseases. However, the effect and mechanism of FGF21 action on cardiac inflammation and fibrosis caused by myocardial injury have rarely been reported. Adult male Sprague-Dawley rats administered with or without recombinant human basic FGF21 (rhbFGF21) were assessed using echocardiography and haematoxylin-eosin and Masson's trichrome staining to determine the cardiac function and cardiac inflammation and fibrosis levels. FGF21 might improve cardiac remodelling, as characterised by a decrease in the expression of a series of inflammatory and fibrosis-related factors. Moreover, when FGF receptors (FGFRs) were blocked, the effects of FGF21 disappeared. Mechanistically, we found that oxidative stress induced the downregulation of early growth response protein 1 (EGR1), which contributed to inflammatory factors and fibrosis reduction in cardiomyocytes treated with H2O2. Collectively, FGF21 effectively suppressed the inflammation and fibrosis in post-infarcted hearts by regulating FGFR-EGR1.

Innate Lymphoid Cells Promote Recovery of Ventricular Function After Myocardial Infarction.

BACKGROUND: Innate lymphoid cells type 2 (ILC2s) play critical homeostatic functions in peripheral tissues. ILC2s reside in perivascular niches and limit atherosclerosis development. OBJECTIVES: ILC2s also reside in the pericardium but their role in postischemic injury is unknown. METHODS: We examined the role of ILC2 in a mouse model of myocardial infarction (MI), and compared mice with or without genetic deletion of ILC2. We determined infarct size using histology and heart function using echocardiography. We assessed cardiac ILC2 using flow cytometry and RNA sequencing. Based on these data, we devised a therapeutic strategy to activate ILC2 in mice with acute MI, using exogenous interleukin (IL)-2. We also assessed the ability of low-dose IL-2 to activate ILC2 in a double-blind randomized clinical trial of patients with acute coronary syndromes (ACS). RESULTS: We found that ILC2 levels were increased in pericardial adipose tissue after experimental MI, and genetic ablation of ILC2 impeded the recovery of heart function. RNA sequencing revealed distinct transcript signatures in ILC2, and pointed to IL-2 axis as a major upstream regulator. Treatment of T-cell-deficient mice with IL-2 (to activate ILC2) significantly improved the recovery of heart function post-MI. Administration of low-dose IL-2 to patients with ACS led to activation of circulating ILC2, with significant increase in circulating IL-5, a prototypic ILC2-derived cytokine. CONCLUSIONS: ILC2s promote cardiac healing and improve the recovery of heart function after MI in mice. Activation of ILC2 using low-dose IL-2 could be a novel therapeutic strategy to promote a reparative response after MI.

Associations Between Inflammation, Cardiovascular Regenerative Capacity, and Cardiovascular Events: A Cohort Study.

Objective: Circulating progenitor cells possess immune modulatory properties and might mitigate inflammation that is characteristic of patients with coronary artery disease. We hypothesized that patients with fewer circulating progenitor cells (CPCs) will have higher inflammatory markers and worse outcomes. Approach and Results: Patients with stable coronary artery disease were enrolled in a prospective study enumerating CPCs as CD (cluster of differentiation)-34-expressing mononuclear cells (CD34+) and inflammation as levels of IL (interleukin)-6 and high-sensitivity CRP (C-reactive protein) levels. Patients were followed for 5 years for the end points of death and myocardial infarction with repeat inflammatory biomarkers measured after a median of 2 years. In the entire cohort of 392 patients, IL-6 and high-sensitivity CRP levels remained unchanged (0.3+/-2.4 pg/mL and 0.1+/-1.0 mg/L; P=0.45) after 2 years. CPC counts (log-transformed) were inversely correlated with the change in IL-6 levels (r, -0.17; P<0.001). Using linear regression, IL-6 and high-sensitivity CRP levels declined by -0.59 (95% CI, -0.90 to -0.20) pg/mL and -0.13 (-0.28 to 0.01) mg/L per 1 log higher CPC counts after adjustment for the demographic and clinical variables, as well as medications. Using Cox models adjusted for these risk factors, a rise in 1 pg/mL of IL-6 was associated with a 11% (95% CI, 9-13) greater risk of death/myocardial infarction. We found that the change in IL6 level partly (by 40%) mediated the higher risk of adverse events among those with low CPC counts. Conclusions: Reduced cardiovascular regenerative capacity is independently associated with progressive inflammation in patients with coronary artery disease that in turn is associated with poor outcomes.

Influenza Vaccination After Myocardial Infarction: A Randomized, Double-Blind, Placebo-Controlled, Multicenter Trial.

BACKGROUND: Observational and small, randomized studies suggest that influenza vaccine may reduce future cardiovascular events in patients with cardiovascular disease. METHODS: We conducted an investigator-initiated, randomized, double-blind trial to compare inactivated influenza vaccine with saline placebo administered shortly after myocardial infarction (MI; 99.7% of patients) or high-risk stable coronary heart disease (0.3%). The primary end point was the composite of all-cause death, MI, or stent thrombosis at 12 months. A hierarchical testing strategy was used for the key secondary end points: all-cause death, cardiovascular death, MI, and stent thrombosis. RESULTS: Because of the COVID-19 pandemic, the data safety and monitoring board recommended to halt the trial before attaining the prespecified sample size. Between October 1, 2016, and March 1, 2020, 2571 participants were randomized at 30 centers across 8 countries. Participants assigned to influenza vaccine totaled 1290 and individuals assigned to placebo equaled 1281; of these, 2532 received the study treatment (1272 influenza vaccine and 1260 placebo) and were included in the modified intention to treat analysis. Over the 12-month follow-up, the primary outcome occurred in 67 participants (5.3%) assigned influenza vaccine and 91 participants (7.2%) assigned placebo (hazard ratio, 0.72 [95% CI, 0.52-0.99]; P=0.040). Rates of all-cause death were 2.9% and 4.9% (hazard ratio, 0.59 [95% CI, 0.39-0.89]; P=0.010), rates of cardiovascular death were 2.7% and 4.5%, (hazard ratio, 0.59 [95% CI, 0.39-0.90]; P=0.014), and rates of MI were 2.0% and 2.4% (hazard ratio, 0.86 [95% CI, 0.50-1.46]; P=0.57) in the influenza vaccine and placebo groups, respectively. CONCLUSIONS: Influenza vaccination early after an MI or in high-risk coronary heart disease resulted in a lower risk of a composite of all-cause death, MI, or stent thrombosis, and a lower risk of all-cause death and cardiovascular death, as well, at 12 months compared with placebo. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02831608.

Role of Neutrophils in Cardiac Injury and Repair Following Myocardial Infarction.

Neutrophils are first-line responders of the innate immune system. Following myocardial infarction (MI), neutrophils are quickly recruited to the ischemic region, where they initiate the inflammatory response, aiming at cleaning up dead cell debris. However, excessive accumulation and/or delayed removal of neutrophils are deleterious. Neutrophils can promote myocardial injury by releasing reactive oxygen species, granular components, and pro-inflammatory mediators. More recent studies have revealed that neutrophils are able to form extracellular traps (NETs) and produce extracellular vesicles (EVs) to aggravate inflammation and cardiac injury. On the contrary, there is growing evidence showing that neutrophils also exert anti-inflammatory, pro-angiogenic, and pro-reparative effects, thus facilitating inflammation resolution and cardiac repair. In this review, we summarize the current knowledge on neutrophils' detrimental roles, highlighting the role of recently recognized NETs and EVs, followed by a discussion of their beneficial effects and molecular mechanisms in post-MI cardiac remodeling. In addition, emerging concepts about neutrophil diversity and their modulation of adaptive immunity are discussed.