Lymphocytic subsets play distinct roles in heart diseases

The roles of Th cells in myocardial infarction

Myocardial infarction, commonly known as a heart attack, is a serious condition caused by the abrupt stoppage of blood flow to a part of the heart, leading to tissue damage. A significant aspect of this condition is reperfusion injury, which occurs when blood flow is restored but exacerbates the damage. This review first addresses the role of the innate immune system, including neutrophils and macrophages, in the cascade of events leading to myocardial infarction and reperfusion injury. It then shifts focus to the critical involvement of CD4+ T helper cells in these processes. These cells, pivotal in regulating the immune response and tissue recovery, include various subpopulations such as Th1, Th2, Th9, Th17, and Th22, each playing a unique role in the pathophysiology of myocardial infarction and reperfusion injury. These subpopulations contribute to the injury process through diverse mechanisms, with cytokines such as IFN-γ and IL-4 influencing the balance between tissue repair and injury exacerbation. Understanding the interplay between the innate immune system and CD4+ T helper cells, along with their cytokines, is crucial for developing targeted therapies to mitigate myocardial infarction and reperfusion injury, ultimately improving outcomes for cardiac patients.

Lymphangiogenesis: A new strategy for heart disease treatment (Review)

Heart disease remains a global health challenge, contributing notably to morbidity and mortality. The lymphatic vasculature, an integral component of the cardiovascular system, plays a crucial role in regulating essential physiological processes, including fluid balance, transportation of extravasated proteins and immune cell trafficking, all of which are important for heart function. Through thorough scientometric analysis and extensive research, the present review identified lymphangiogenesis as a hotspot in cardiovascular disease research, and the mechanisms underlying impaired cardiac lymphangiogenesis and inadequate lymph drainage in various cardiovascular diseases are discussed. Furthermore, the way used to improve lymphangiogenesis to effectively regulate a variety of heart diseases and associated signaling pathways was investigated. Notably, the current review also highlights the impact of Traditional Chinese Medicine (TCM) on lymphangiogenesis, aiming to establish a clinical basis for the potential of TCM to improve cardiovascular diseases by promoting lymphangiogenesis.

Cardiac fibrogenesis: an immuno-metabolic perspective

Cardiac fibrosis is a major and complex pathophysiological process that ultimately culminates in cardiac dysfunction and heart failure. This phenomenon includes not only the replacement of the damaged tissue by a fibrotic scar produced by activated fibroblasts/myofibroblasts but also a spatiotemporal alteration of the structural, biochemical, and biomechanical parameters in the ventricular wall, eliciting a reactive remodeling process. Though mechanical stress, post-infarct homeostatic imbalances, and neurohormonal activation are classically attributed to cardiac fibrosis, emerging evidence that supports the roles of immune system modulation, inflammation, and metabolic dysregulation in the initiation and progression of cardiac fibrogenesis has been reported. Adaptive changes, immune cell phenoconversions, and metabolic shifts in the cardiac nonmyocyte population provide initial protection, but persistent altered metabolic demand eventually contributes to adverse remodeling of the heart. Altered energy metabolism, mitochondrial dysfunction, various immune cells, immune mediators, and cross-talks between the immune cells and cardiomyocytes play crucial roles in orchestrating the transdifferentiation of fibroblasts and ensuing fibrotic remodeling of the heart. Manipulation of the metabolic plasticity, fibroblast-myofibroblast transition, and modulation of the immune response may hold promise for favorably modulating the fibrotic response following different cardiovascular pathological processes. Although the immunologic and metabolic perspectives of fibrosis in the heart are being reported in the literature, they lack a comprehensive sketch bridging these two arenas and illustrating the synchrony between them. This review aims to provide a comprehensive overview of the intricate relationship between different cardiac immune cells and metabolic pathways as well as summarizes the current understanding of the involvement of immune-metabolic pathways in cardiac fibrosis and attempts to identify some of the previously unaddressed questions that require further investigation. Moreover, the potential therapeutic strategies and emerging pharmacological interventions, including immune and metabolic modulators, that show promise in preventing or attenuating cardiac fibrosis and restoring cardiac function will be discussed.

Exercise Inhibits Doxorubicin-Induced Cardiotoxicity via Regulating B Cells

BACKGROUND

Doxorubicin is an effective chemotherapeutic agent, but its use is limited by acute and chronic cardiotoxicity. Exercise training has been shown to protect against doxorubicin-induced cardiotoxicity, but the involvement of immune cells remains unclear. This study aimed to investigate the role of exercise-derived B cells in protecting against doxorubicin-induced cardiotoxicity and to further determine whether B cell activation and antibody secretion play a role in this protection.

METHODS

Mice that were administered with doxorubicin (5 mg/kg per week, 20 mg/kg cumulative dose) received treadmill running exercise. The adoptive transfer of exercise-derived splenic B cells to μMT-/- (B cell-deficient) mice was performed to elucidate the mechanism of B cell regulation that mediated the effect of exercise.

RESULTS

Doxorubicin-administered mice that had undergone exercise training showed improved cardiac function, and low levels of cardiac apoptosis, atrophy, and fibrosis, and had reduced cardiac antibody deposition and proinflammatory responses. Similarly, B cell pharmacological and genetic depletion alleviated doxorubicin-induced cardiotoxicity, which phenocopied the protection of exercise. In vitro performed coculture experiments confirmed that exercise-derived B cells reduced cardiomyocyte apoptosis and fibroblast activation compared with control B cells. Importantly, the protective effect of exercise on B cells was confirmed by the adoptive transfer of splenic B cells from exercised donor mice to μMT-/- recipient mice. However, blockage of Fc gamma receptor IIB function using B cell transplants from exercised Fc gamma receptor IIB-/- mice abolished the protection of exercise-derived B cells against doxorubicin-induced cardiotoxicity. Mechanistically, we found that Fc gamma receptor IIB, an important B cell inhibitory receptor, responded to exercise and increased B cell activation threshold, which participated in exercise-induced protection against doxorubicin-induced cardiotoxicity.

CONCLUSIONS

Our results demonstrate that exercise training protects against doxorubicin-induced cardiotoxicity by upregulating Fc gamma receptor IIB expression in B cells, which plays an important anti-inflammatory role and participates in the protective effect of exercise against doxorubicin-induced cardiotoxicity.

Immune cells and related cytokines in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is a non-ischemic cardiomyopathy involving one or more underlying etiologies. It is characterized by structural and functional dysfunction of the myocardium, potentially leading to fibrosis and ventricular remodeling, and an elevated risk of heart failure (HF). Although the pathogenesis of DCM remains unknown, compelling evidence suggests that DCM-triggered immune cells and inflammatory cascades play a crucial role in the occurrence and development of DCM. Various factors are linked to myocardial damage, inducing aberrant activation of the immune system and sustained inflammatory responses in DCM. The investigation of the immunopathogenesis of DCM also contributes to discovering new biomarkers and therapeutic targets. This review examines the roles of immune cells and related cytokines in DCM pathogenesis and explores immunotherapy strategies in DCM.

CardiOmics signatures reveal therapeutically actionable targets and drugs for cardiovascular diseases

Cardiovascular diseases are the leading cause of death worldwide, with heart failure being a complex condition that affects millions of individuals. Single-nucleus RNA sequencing has recently emerged as a powerful tool for unraveling the molecular mechanisms behind cardiovascular diseases. This cutting-edge technology enables the identification of molecular signatures, intracellular networks, and spatial relationships among cardiac cells, including cardiomyocytes, mast cells, lymphocytes, macrophages, lymphatic endothelial cells, endocardial cells, endothelial cells, epicardial cells, adipocytes, fibroblasts, neuronal cells, pericytes, and vascular smooth muscle cells. Despite these advancements, the discovery of essential therapeutic targets and drugs for precision cardiology remains a challenge. To bridge this gap, we conducted comprehensive in silico analyses of single-nucleus RNA sequencing data, functional enrichment, protein interactome network, and identification of the shortest pathways to physiological phenotypes. This integrated multi-omics analysis generated CardiOmics signatures, which allowed us to pinpoint three therapeutically actionable targets (ADRA1A1, PPARG, and ROCK2) and 15 effective drugs, including adrenergic receptor agonists, adrenergic receptor antagonists, norepinephrine precursors, PPAR receptor agonists, and Rho-associated kinase inhibitors, involved in late-stage cardiovascular disease clinical trials.

The Role of «Novel» Biomarkers of Systemic Inflammation in the Development of Early Hospital Events after Aortic Valve Replacement in Patients with Aortic Stenosis

INTRODUCTION

The pathogenesis of aortic stenosis includes the processes of chronic inflammation, calcification, lipid metabolism disorders, and congenital structural changes. The goal of our study was to determine the predictive value of novel biomarkers of systemic inflammation and some hematological indices based on the numbers of leukocytes and their subtypes in the development of early hospital medical conditions after mechanical aortic valve replacement in patients with aortic stenosis.

MATERIALS AND METHODS

This was a cohort study involving 363 patients who underwent surgical intervention for aortic valve pathology between 2014 and 2020. The following markers of systemic inflammation and hematological indices were studied: SIRI (Systemic Inflammation Response Index), SII (Systemic Inflammation Index), AISI (Aggregate Index of Systemic Inflammation), NLR (Neutrophil/Lymphocyte Ratio), PLR (Platelet/Lymphocyte Ratio), and MLR (Monocyte/Lymphocyte Ratio). Associations of the levels of these biomarkers and indices with the development of in-hospital death, acute kidney injury, postoperative atrial fibrillation, stroke/acute cerebrovascular accident, and bleeding were calculated.

RESULTS

According to an ROC analysis, an SIRI > 1.5 (p < 0.001), an SII > 718 (p = 0.002), an AISI > 593 (p < 0.001), an NLR > 2.48 (p < 0.001), a PLR > 132 (p = 0.004), and an MLR > 0.332 (p < 0.001) were statistically significantly associated with in-hospital death. Additionally, an SIRI > 1.5 (p < 0.001), an NLR > 2.8 (p < 0.001), and an MLR > 0.392 (p < 0.001) were associated with bleeding in the postoperative period. In a univariate logistic regression, SIRI, SII, AISI, and NLR were statistically significant independent factors associated with in-hospital death. In a multivariate logistic regression model, SIRI was the most powerful marker of systemic inflammation.

CONCLUSION

SIRI, SII, AISI, and NLR as novel biomarkers of systemic inflammation were associated with in-hospital mortality. Of all markers and indices of systemic inflammation in our study, SIRI was the strongest predictor of a poor outcome in the multivariate regression model.

Reduced numbers of regulatory T cells in chronic heart failure seems not to be restored by cardiac resynchronization therapy

BACKGROUND

T cells have been implicated in the development and progression of inflammatory processes in chronic heart failure (CHF). Cardiac resynchronization therapy (CRT) has beneficial effects on symptoms and cardiac remodeling in CHF. However, its impact on the inflammatory immune response remains controversial. We aimed to study the impact of CRT on T cells in heart failure (HF) patients.

METHODS

Thirty-nine HF patients were evaluated before CRT (T0) and six months later (T6). Quantification of T cells, their subsets, and their functional characterization, after in vitro stimulation, were evaluated by flow cytometry.

RESULTS

T regulatory (Treg) cells were decreased in CHF patients (healthy group (HG): 1.08 ± 0.50 versus (heart failure patients (HFP)-T0: 0.69 ± 0.40, P = 0.022) and remaining diminished after CRT (HFP-T6: 0.61 ± 0.29, P = 0.003). Responders (R) to CRT presented a higher frequency of T cytotoxic (Tc) cells producing IL-2 at T0 compared with non-responders (NR) (R: 36.52 ± 12.55 versus NR: 24.71 ± 11.66, P = 0.006). After CRT, HF patients presented a higher percentage of Tc cells expressing TNF-α and IFN-γ (HG: 44.50 ± 16.62 versus R: 61.47 ± 20.54, P = 0.014; and HG: 40.62 ± 15.36 versus R: 52.39 ± 18.66, P = 0.049, respectively).

CONCLUSION

The dynamic of different functional T cell subpopulations is significantly altered in CHF, which results in an exacerbated pro-inflammatory response. Even after CRT, it seems that the inflammatory condition underlying CHF continues to evolve with the progression of the disease. This could be due, at least in part, to the inability to restore Treg cells levels.

TRIAL REGISTRATION

Observational and prospective study with no trial registration.

Beyond cardiomyocytes: Cellular diversity in the heart's response to exercise

Cardiomyocytes comprise ∼70% to 85% of the total volume of the adult mammalian heart but only about 25% to 35% of its total number of cells. Advances in single cell and single nuclei RNA sequencing have greatly facilitated investigation into and increased appreciation of the potential functions of non-cardiomyocytes in the heart. While much of this work has focused on the relationship between non-cardiomyocytes, disease, and the heart's response to pathological stress, it will also be important to understand the roles that these cells play in the healthy heart, cardiac homeostasis, and the response to physiological stress such as exercise. The present review summarizes recent research highlighting dynamic changes in non-cardiomyocytes in response to the physiological stress of exercise. Of particular interest are changes in fibrotic pathways, the cardiac vasculature, and immune or inflammatory cells. In many instances, limited data are available about how specific lineages change in response to exercise or whether the changes observed are functionally important, underscoring the need for further research.

Value of the systemic immune-inflammation index in predicting poor postoperative outcomes and the short-term prognosis of heart valve diseases: a retrospective cohort study

OBJECTIVE

Systemic immune-inflammation index (SII) is a novel biomarker that can predict poor outcomes in tumours, nervous system diseases and chronic heart failure. Here, we investigated the predictive value of SII on the poor postoperative outcomes and short-term prognosis of heart valve diseases (HVDs).

DESIGN, SETTING AND PARTICIPANTS

This retrospective cohort study enrolled all consecutive patients with HVDs (aortic stenosis, aortic regurgitation, mitral stenosis and mitral regurgitation) who underwent surgery (valve replacement or valve repair) at the Affiliated Hospital of North Sichuan Medical College between 2017 and 2020.

MAIN OUTCOMES AND MEASURES

Major complications in the perioperative period, all-cause mortality within 30 days and readmission within 30 days.

RESULTS

A total of 431 patients with HVDs were enrolled in this study, including 202 males and 229 females, aged 58.9±27.3 years. SII levels of patients in the poor outcomes group were significantly higher than those of patients in the favourable outcomes group (658.40±436.29 vs 335.72±174.76, respectively; p<0.001). Multivariate logistic regression analysis showed that age (OR 1.064, 95% CI 1.026 to 1.104, p=0.025), SII (OR 1.034, 95% CI 1.012 to 1.631, p=0.008) and aortic cross-clamping time (OR 1.013, 95% CI 1.004 to 1.023, p=0.006) were independent risk factors for poor outcomes and short-term prognosis in patients with HVD. The area under the curve of poor outcomes predicted by SII in patients with HVD was 0.806 (95% CI 0.763 to 0.848) and the optimised cut-off value 423.8×10⁹ /L, with a sensitivity of 70.3% and specificity of 81.1%. The incidence of poor outcomes (p<0.001), 30-day mortality (p<0.001) and 30-day readmission rate (p=0.026) in the high SII group was significantly higher than that in the low SII group.

CONCLUSIONS

SII is closely related to poor postoperative outcomes and short-term prognosis of HVD and can serve as an independent predictive factor.

The prognostic value of admission lymphocyte-to-monocyte ratio in critically ill patients with acute myocardial infarction

Background

Inflammation plays a critical role in acute myocardial infarction (AMI). Recent studies have shown the value of hematologic indicators in MI risk stratification and prognostic assessment. However, the association between lymphocyte-to-monocyte ratio (LMR) and the long-term mortality of critically ill MI patients remains unclear.

Methods

Clinical data were extracted from the Medical Information Mart for Intensive Care III database. Patients diagnosed with AMI on admission in the intensive care units were include. The optimal cutoff value of LMR was determined by X-tile software. The Cox proportional hazard model was applied for the identification of independent prognostic factors of 1-year mortality and survival curves were estimated using the Kaplan–Meier method. In order to reduce selection bias, a 1:1 propensity score matching (PSM) method was performed.

Results

A total of 1517 AMI patients were included in this study. The cutoff value for 1-year mortality of LMR determined by X-Tile software was 3.00. A total of 534 pairs of patients were matched after PSM. Multivariate analysis (HR = 1.369, 95%CI 1.110–1.687, P = 0.003) and PSM subgroups (HR = 1.299, 95%CI 1.032–1.634, P = 0.026) showed that 1-year mortality was significantly higher in patients with LMR < 3.00 than patients with LMR ≥ 3.00 in Cox proportional hazard models. The survival curves showed that patients with LMR < 3.00 had a significantly lower 1-year survival rate before (63.83 vs. 81.03%, Log rank P < 0.001) and after PSM (68.13 vs. 74.22%, Log rank P = 0.041).

Conclusion

In this retrospective cohort analysis, we demonstrated that a low admission LMR (< 3.00) was associated with a higher risk of 1-year mortality in critically ill patients with AMI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02745-z.

Immune cell metabolism and metabolic reprogramming

Energy metabolism maintains the activation of intracellular and intercellular signal transduction, and plays a crucial role in immune response. Under environmental stimulation, immune cells change from resting to activation and trigger metabolic reprogramming. The immune system cells exhibit different metabolic characteristics when performing functions. The study of immune metabolism provides new insights into the function of immune cells, including how they differentiate, migrate and exert immune responses. Studies of immune cell energy metabolism are beginning to shed light on the metabolic mechanism of disease progression and reveal new ways to target inflammatory diseases such as autoimmune diseases, chronic viral infections, and cancer. Here, we discussed the relationship between immune cells and metabolism, and proposed the possibility of targeted metabolic process for disease treatment.

When a Friend Becomes Your Enemy: Natural Killer Cells in Atherosclerosis and Atherosclerosis-Associated Risk Factors

Atherosclerosis (ATS), the change in structure and function of arteries with associated lesion formation and altered blood flow, is the leading cause of cardiovascular disease, the number one killer worldwide. Beyond dyslipidemia, chronic inflammation, together with aberrant phenotype and function of cells of both the innate and adaptive immune system, are now recognized as relevant contributors to atherosclerosis onset and progression. While the role of macrophages and T cells in atherosclerosis has been addressed in several studies, Natural Killer cells (NKs) represent a poorly explored immune cell type, that deserves attention, due to NKs’ emerging contribution to vascular homeostasis. Furthermore, the possibility to re-polarize the immune system has emerged as a relevant tool to design new therapies, with some succesfull exmples in the field of cancer immunotherapy. Thus, a deeper knowledge of NK cell pathophysiology in the context of atherosclerosis and atherosclerosis-associated risk factors could help developing new preventive and treatment strategies, and decipher the complex scenario/history from “the risk factors for atherosclerosis” Here, we review the current knowledge about NK cell phenotype and activities in atherosclerosis and selected atherosclerosis risk factors, namely type-2 diabetes and obesity, and discuss the related NK-cell oriented environmental signals.

Management of inflammation in cardiovascular diseases

Cardiovascular disease is the leading cause of morbidity and mortality world-wide. Recently, the role of inflammation in the progression of diseases has significantly attracted considerable attention. In addition, various comorbidities, including diabetes, obesity, etc. exacerbate inflammation in the cardiovascular system, which ultimately leads to heart failure. Furthermore, cytokines released from specialized immune cells are key mediators of cardiac inflammation. Here, in this review article, we focused on the role of selected immune cells and cytokines (both pro-inflammatory and anti-inflammatory) in the regulation of cardiac inflammation and ultimately in cardiovascular diseases. While IL-1β, IL-6, TNFα, and IFNγ are associated with cardiac inflammation; IL-10, TGFβ, etc. are associated with resolution of inflammation and cardiac repair. IL-10 reduces cardiovascular inflammation and protects the cardiovascular system via interaction with SMAD2, p53, HuR, miR-375 and miR-21 pathway. In addition, we also highlighted recent advancements in the management of cardiac inflammation, including clinical trials of anti-inflammatory molecules to alleviate cardiovascular diseases.

Sengers syndrome: a rare case of cardiomyopathy combined with congenital cataracts in an infant: post-mortem case report

Sengers syndrome is a rare autosomal recessive disorder caused by a mutation in the Acylglycerol Kinase (AGK) gene with subsequent mitochondrial dysfunction. It is a combination of cardiomyopathy, skeletal myopathy, congenital bilateral cataracts, and lactic acidosis following exertion. The current study describes an extremely rare case of Sengers syndrome that is diagnosed during post-mortem examination. A four-month-old female child underwent sudden cardiac arrest immediately following the induction of general anesthesia for lens extraction surgery. This infant was the first child born to healthy, non-consanguineous, Egyptian parents. There were unremarkable medical problems either during pregnancy or during delivery. This infant was born at term with a normal APGAR score and weight. She had congenital bilateral cataracts since birth, easily-fatigued, and delayed milestones for her age. A post-mortem examination revealed a hypertrophied heart that weighed 96.6 grams with left ventricular hypertrophy. The left ventricle free wall thickness was 1cm, and an interventricular septum thickness of 1.3 cm. Histopathologically, the myocardium showed myocytes disarray. Also, the myocytes were hypertrophied, and vacuolated. The Gömöri trichrome stain revealed vacuolated cardiomyocytes surrounded by collagenous connective tissue, and the Periodic Acid Schiff (PAS) stain excluded that these vacuolations were related to glycogen storage disease. Focal lymphocytic infiltrations were observed within the myocardium. Thus, Sengers syndrome should be taken into consideration as a possible diagnosis whenever a congenital cataract is present for clinical and medicolegal cases.

Understanding the Adult Mammalian Heart at Single-Cell RNA-Seq Resolution

During the last decade, extensive efforts have been made to comprehend cardiac cell genetic and functional diversity. Such knowledge allows for the definition of the cardiac cellular interactome as a reasonable strategy to increase our understanding of the normal and pathologic heart. Previous experimental approaches including cell lineage tracing, flow cytometry, and bulk RNA-Seq have often tackled the analysis of cardiac cell diversity as based on the assumption that cell types can be identified by the expression of a single gene. More recently, however, the emergence of single-cell RNA-Seq technology has led us to explore the diversity of individual cells, enabling the cardiovascular research community to redefine cardiac cell subpopulations and identify relevant ones, and even novel cell types, through their cell-specific transcriptomic signatures in an unbiased manner. These findings are changing our understanding of cell composition and in consequence the identification of potential therapeutic targets for different cardiac diseases. In this review, we provide an overview of the continuously changing cardiac cellular landscape, traveling from the pre-single-cell RNA-Seq times to the single cell-RNA-Seq revolution, and discuss the utilities and limitations of this technology.

Does the Global Outbreak of COVID-19 or Other Viral Diseases Threaten the Stem Cell Reservoir Inside the Body?

The COVID-19 pandemic has profoundly influenced public health and contributed to global economic divergences of unprecedented dimensions. Due to the high prevalence and mortality rates, it is then expected that the consequence and public health challenges will last for long periods. The rapid global spread of COVID-19 and lack of enough data regarding the virus pathogenicity multiplies the complexity and forced governments to react quickly against this pandemic. Stem cells represent a small fraction of cells located in different tissues. These cells play a critical role in the regeneration and restoration of injured sites. Because of their specific niche and a limited number of stem cells, the key question is whether there are different anti-viral mechanisms against viral infection notably COVID-19. Here, we aimed to highlight the intrinsic antiviral resistance in different stem cells against viral infection. These data could help us to understand the possible viral infections in different stem cells and the activation of specific molecular mechanisms upon viral entrance.

The Dynamic Interplay Between Cardiac Inflammation and Fibrosis

Heart failure is a leading cause of death worldwide. While there are multiple etiologies contributing to the development of heart failure, all cause result in impairments in cardiac function that is characterized by changes in cardiac remodeling and compliance. Fibrosis is associated with nearly all forms of heart failure and is an important contributor to disease pathogenesis. Inflammation also plays a critical role in the heart and there is a large degree of interconnectedness between the inflammatory and fibrotic response. This review discusses the cellular and molecular mechanisms contributing to inflammation and fibrosis and the interplay between the two.

Leukocyte-Dependent Regulation of Cardiac Fibrosis

Cardiac fibrosis begins as an intrinsic response to injury or ageing that functions to preserve the tissue from further damage. Fibrosis results from activated cardiac myofibroblasts, which secrete extracellular matrix (ECM) proteins in an effort to replace damaged tissue; however, excessive ECM deposition leads to pathological fibrotic remodeling. At this extent, fibrosis gravely disturbs myocardial compliance, and ultimately leads to adverse outcomes like heart failure with heightened mortality. As such, understanding the complexity behind fibrotic remodeling has been a focal point of cardiac research in recent years. Resident cardiac fibroblasts and activated myofibroblasts have been proven integral to the fibrotic response; however, several findings point to additional cell types that may contribute to the development of pathological fibrosis. For one, leukocytes expand in number after injury and exhibit high plasticity, thus their distinct role(s) in cardiac fibrosis is an ongoing and controversial field of study. This review summarizes current findings, focusing on both direct and indirect leukocyte-mediated mechanisms of fibrosis, which may provide novel targeted strategies against fibrotic remodeling.