Impairment of monocyte-derived dendritic cells in idiopathic pulmonary arterial hypertension

Role of angiotensin converting enzyme in pathogenesis associated with immunity in cardiovascular diseases

Angiotensin converting enzyme (ACE) is not only a critical component in the renin-angiotensin system (RAS), but also suggested as an important mediator for immune response and activity, such as immune cell mobilization, metabolism, biogenesis of immunoregulatory molecules, etc. The chronic duration of cardiovascular diseases (CVD) has been increasingly considered to be triggered by uncontrolled pathologic immune reactions from myeloid cells and lymphocytes. Considering the potential anti-inflammatory effect of the traditional antihypertensive ACE inhibitor (ACEi), we attempt to elucidate whether ACE and its catalytically relevant substances as well as signaling pathways play a role in the immunity-related pathogenesis of common CVD, such as arterial hypertension, atherosclerosis and arrythmias. ACEi was also reported to benefit the prognoses of COVID-19-positive patients with CVD, and COVID-19 disease with preexisting CVD or subsequent cardiovascular damage is featured by a significant influx of immune cells and proinflammatory molecules, suggesting that ACE may also participate in COVID-19 induced cardiovascular injury, because COVID-19 disease basically triggers an overactive pathologic immune response. Hopefully, the ACE inhibition and manipulation of those associated bioactive signals could supplement the current medicinal management of various CVD and bring greater benefit to patients' cardiovascular health.

Bibliometric analysis of T-cells immunity in pulmonary hypertension from 1992 to 2022

BACKGROUND

Adaptive immunity is an important disease mediator of pulmonary vascular remodeling during pulmonary hypertension (PH) development, especially T-cells lymphocytes. However, data for bibliometric analysis of T cell immunity in PH is currently vacant. This aimed to provide a comprehensive and visualized view of T-cells research in PH pathogenesis and to lay a solid foundation for further studies.

METHODS

The data was acquired from the Web of Science Core Collection database. Web of Science analytic tool was used to analysis the publication years, authors, journals, countries, and organizations. CiteSpace 6.2.R3, VOSviewer 1.6.16, and Scimago Graphica 1.0.35.0 were applied to conduct a visualization bibliometric analysis about authors, countries, institutions, journals, references, and keywords.

RESULTS

Nine hundred and eight publications from 1992 to 2022 were included in the analysis. The results showed that Humbert Marc was the most prolific author. American Journal of Physiology Lung Cellular and Molecular Physiology had the most related articles. The institution with the most articles was Udice French Research University. The United States was far ahead in the article output. Keywords analysis showed that "Pulmonary hypertension" was the most usually appeared keyword in the relevant literature, and included "T-cells", "Regulatory T cells", and "Activated T cell." "miRNA" of reference co-citation clustering analysis demonstrated the possible T-cell immunity activation mechanisms in PH. The most cited literature was published in the European Heart Journal by Galie N in 2016. The strongest citation burst of keyword is "gene expression" and terms such as "vascular remodeling," "growth," "proliferation," and "fibrosis" are among the list, indicating that T-cells interact with stromal vascular cells to induce pulmonary vascular remodeling. The strongest burst of cited reference is "Galie N, 2016."

CONCLUSIONS

T-cell immunity is an important pathogenesis mechanism for PH development, which may have interaction with miRNAs and stromal vascular cells, but the possible T-cell immunity activation mechanisms in PH need to be investigated further.

The role of immune cells and inflammation in pulmonary hypertension: mechanisms and implications

Pulmonary hypertension (PH) is a malignant disease with progressive increase of pulmonary vascular pressure, which eventually leads to right heart failure. More and more evidences show that immune cells and inflammation play an important role in the occurrence and development of PH. In the context of pulmonary vascular diseases, immune cells migrate into the walls of the pulmonary vascular system. This leads to an increase in the levels of cytokines and chemokines in both the bloodstream and the surrounding tissues of the pulmonary vessels. As a result, new approaches such as immunotherapy and anti-inflammatory treatments are being considered as potential strategies to halt or potentially reverse the progression of PH. We reviewed the potential mechanisms of immune cells, cytokines and chemokines in PH development. The potential relationship of vascular cells or bone morphogenetic protein receptor 2 (BMPR2) in immune regulation was also expounded. The clinical application and future prospect of immunotherapy were further discussed.

Inflammation and immunity in the pathogenesis of hypoxic pulmonary hypertension

Hypoxic pulmonary hypertension (HPH) is a complicated vascular disorder characterized by diverse mechanisms that lead to elevated blood pressure in pulmonary circulation. Recent evidence indicates that HPH is not simply a pathological syndrome but is instead a complex lesion of cellular metabolism, inflammation, and proliferation driven by the reprogramming of gene expression patterns. One of the key mechanisms underlying HPH is hypoxia, which drives immune/inflammation to mediate complex vascular homeostasis that collaboratively controls vascular remodeling in the lungs. This is caused by the prolonged infiltration of immune cells and an increase in several pro-inflammatory factors, which ultimately leads to immune dysregulation. Hypoxia has been associated with metabolic reprogramming, immunological dysregulation, and adverse pulmonary vascular remodeling in preclinical studies. Many animal models have been developed to mimic HPH; however, many of them do not accurately represent the human disease state and may not be suitable for testing new therapeutic strategies. The scientific understanding of HPH is rapidly evolving, and recent efforts have focused on understanding the complex interplay among hypoxia, inflammation, and cellular metabolism in the development of this disease. Through continued research and the development of more sophisticated animal models, it is hoped that we will be able to gain a deeper understanding of the underlying mechanisms of HPH and implement more effective therapies for this debilitating disease.

Lasso algorithm and support vector machine strategy to screen pulmonary arterial hypertension gene diagnostic markers

BACKGROUND

This study employs machine learning strategy algorithms to screen the optimal gene signature of pulmonary arterial hypertension (PAH) under big data in the medical field.

METHODS

The public database Gene Expression Omnibus (GEO) was used to analyze datasets of 32 normal controls and 37 PAH disease samples. The enrichment analysis was performed after selecting the differentially expressed genes. Two machine learning methods, the least absolute shrinkage and selection operator (LASSO) and support vector machine (SVM), were used to identify the candidate genes. The external validation data set further tests the expression level and diagnostic value of candidate diagnostic genes. The diagnostic effectiveness was evaluated by obtaining the receiver operating characteristic curve (ROC). The convolution tool CIBERSORT was used to estimate the composition pattern of the immune cell subtypes and to perform correlation analysis based on the combined training dataset.

RESULTS

A total of 564 differentially expressed genes (DEGs) were screened in normal control and pulmonary hypertension samples. The enrichment analysis results were found to be closely related to cardiovascular diseases, inflammatory diseases, and immune-related pathways. The LASSO and SVM algorithms in machine learning used 5 × cross-validation to identify 9 and 7 characteristic genes. The two machine learning algorithms shared Caldesmon 1 (CALD1) and Solute Carrier Family 7 Member 11 (SLC7A11) as genetic signals highly correlated with PAH. The results showed that the area under ROC (AUC) of the specific characteristic diagnostic genes were CALD1 (AUC = 0.924) and SLC7A11 (AUC = 0.962), indicating that the two diagnostic genes have high diagnostic value.

CONCLUSION

CALD1 and SLC7A11 can be used as diagnostic markers of PAH to obtain new insights for the further study of the immune mechanism involved in PAH.

Pulmonary hypertension: Linking inflammation and pulmonary arterial stiffening

Pulmonary hypertension (PH) is a progressive disease that arises from multiple etiologies and ultimately leads to right heart failure as the predominant cause of morbidity and mortality. In patients, distinct inflammatory responses are a prominent feature in different types of PH, and various immunomodulatory interventions have been shown to modulate disease development and progression in animal models. Specifically, PH-associated inflammation comprises infiltration of both innate and adaptive immune cells into the vascular wall of the pulmonary vasculature—specifically in pulmonary vascular lesions—as well as increased levels of cytokines and chemokines in circulating blood and in the perivascular tissue of pulmonary arteries (PAs). Previous studies suggest that altered hemodynamic forces cause lung endothelial dysfunction and, in turn, adherence of immune cells and release of inflammatory mediators, while the resulting perivascular inflammation, in turn, promotes vascular remodeling and the progression of PH. As such, a vicious cycle of endothelial activation, inflammation, and vascular remodeling may develop and drive the disease process. PA stiffening constitutes an emerging research area in PH, with relevance in PH diagnostics, prognostics, and as a therapeutic target. With respect to its prognostic value, PA stiffness rivals the well-established measurement of pulmonary vascular resistance as a predictor of disease outcome. Vascular remodeling of the arterial extracellular matrix (ECM) as well as vascular calcification, smooth muscle cell stiffening, vascular wall thickening, and tissue fibrosis contribute to PA stiffening. While associations between inflammation and vascular stiffening are well-established in systemic vascular diseases such as atherosclerosis or the vascular manifestations of systemic sclerosis, a similar connection between inflammatory processes and PA stiffening has so far not been addressed in the context of PH. In this review, we discuss potential links between inflammation and PA stiffening with a specific focus on vascular calcification and ECM remodeling in PH.

FAM171B as a Novel Biomarker Mediates Tissue Immune Microenvironment in Pulmonary Arterial Hypertension

The purpose of this study was to uncover potential diagnostic indicators of pulmonary arterial hypertension (PAH), evaluate the function of immune cells in the pathogenesis of the disease, and find innovative treatment targets and medicines with the potential to enhance prognosis. Gene Expression Omnibus was utilized to acquire the PAH datasets. We recognized differentially expressed genes (DEGs) and investigated their functions utilizing R software. Weighted gene coexpression network analysis, least absolute shrinkage and selection operators, and support vector machines were used to identify biomarkers. The extent of immune cell infiltration in the normal and PAH tissues was determined using CIBERSORT. Additionally, the association between diagnostic markers and immune cells was analyzed. In this study, 258DEGs were used to analyze the disease ontology. Most DEGs were linked with atherosclerosis, arteriosclerotic cardiovascular disease, and lung disease, including obstructive lung disease. Gene set enrichment analysis revealed that compared to normal samples, results from PAH patients were mostly associated with ECM-receptor interaction, arrhythmogenic right ventricular cardiomyopathy, the Wnt signaling pathway, and focal adhesion. FAM171B was identified as a biomarker for PAH (area under the curve = 0.873). The mechanism underlying PAH may be mediated by nave CD4 T cells, resting memory CD4 T cells, resting NK cells, monocytes, activated dendritic cells, resting mast cells, and neutrophils, according to an investigation of immune cell infiltration. FAM171B expression was also associated with resting mast cells, monocytes, and CD8 T cells. The results suggest that PAH may be closely related to FAM171B with high diagnostic performance and associated with immune cell infiltration, suggesting that FAM171B may promote the progression of PAH by stimulating immune infiltration and immune response. This study provides valuable insights into the pathogenesis and treatment of PAH.

Peripheral Blood T Cells of Patients with IPAH Have a Reduced Cytokine-Producing Capacity

Pulmonary arterial hypertension (PAH) is rare disease that is categorized as idiopathic (IPAH) when no underlying cause can be identified. Lungs of most patients with IPAH contain increased numbers of T cells and dendritic cells (DCs), suggesting involvement of the immune system in its pathophysiology. However, our knowledge on circulating immune cells in IPAH is rather limited. We used flow cytometry to characterize peripheral blood DCs and T cells in treatment-naive IPAH patients, compared with connective-tissue disease-PAH (CTD-PAH) patients and healthy controls (HCs). At diagnosis, T-helper (Th) cells of IPAH patients were less capable of producing TNFα, IFNγ, IL-4 and IL-17 compared to HCs. IPAH patients showed a decreased frequency of Th2 cells and significantly enhanced expression of the CTLA4 checkpoint molecule in naive CD4⁺ T cells and both naive and memory CD8⁺ T cells. Frequencies and surface marker expression of circulating DCs and monocytes were essentially comparable between IPAH patients and HCs. Principal component analysis (PCA) separated IPAH patients—but not CTD-PAH patients—from HCs, based on T-cell cytokine profiles. At 1-year follow-up, the frequencies of IL-17⁺ production by memory CD4⁺ T cells were increased in IPAH patients and accompanied by increased proportions of Th17 and Tc17 cells, as well as decreased CTLA4 expression. Treatment-naive IPAH patients displayed a unique T-cell phenotype that was different from CTD-PAH patients and was characterized by reduced cytokine-producing capacity. These findings point to involvement of adaptive immune responses in IPAH, which may have an implication for the development of therapeutic interventions.

Dysregulated Immunity in Pulmonary Hypertension: From Companion to Composer

Pulmonary hypertension (PH) represents a grave condition associated with high morbidity and mortality, emphasizing a desperate need for innovative and targeted therapeutic strategies. Cumulative evidence suggests that inflammation and dysregulated immunity interdependently affect maladaptive organ perfusion and congestion as hemodynamic hallmarks of the pathophysiology of PH. The role of altered cellular and humoral immunity in PH gains increasing attention, especially in pulmonary arterial hypertension (PAH), revealing novel mechanistic insights into the underlying immunopathology. Whether these immunophysiological aspects display a universal character and also hold true for other types of PH (e.g., PH associated with left heart disease, PH-LHD), or whether there are unique immunological signatures depending on the underlying cause of disease are points of consideration and discussion. Inflammatory mediators and cellular immune circuits connect the local inflammatory landscape in the lung and heart through inter-organ communication, involving, e.g., the complement system, sphingosine-1-phosphate (S1P), cytokines and subsets of, e.g., monocytes, macrophages, natural killer (NK) cells, dendritic cells (DCs), and T- and B-lymphocytes with distinct and organ-specific pro- and anti-inflammatory functions in homeostasis and disease. Perivascular macrophage expansion and monocyte recruitment have been proposed as key pathogenic drivers of vascular remodeling, the principal pathological mechanism in PAH, pinpointing toward future directions of anti-inflammatory therapeutic strategies. Moreover, different B- and T-effector cells as well as DCs may play an important role in the pathophysiology of PH as an imbalance of T-helper-17-cells (T_H17) activated by monocyte-derived DCs, a potentially protective role of regulatory T-cells (T_reg) and autoantibody-producing plasma cells occur in diverse PH animal models and human PH. This article highlights novel aspects of the innate and adaptive immunity and their interaction as disease mediators of PH and its specific subtypes, noticeable inflammatory mediators and summarizes therapeutic targets and strategies arising thereby.

Autoimmunity in Pulmonary Arterial Hypertension: Evidence for Local Immunoglobulin Production

Pulmonary arterial hypertension (PAH) is a progressive life-threatening disease. The notion that autoimmunity is associated with PAH is widely recognized by the observations that patients with connective tissue diseases or virus infections are more susceptible to PAH. However, growing evidence supports that the patients with idiopathic PAH (IPAH) with no autoimmune diseases also have auto-antibodies. Anti-inflammatory therapy shows less help in decreasing auto-antibodies, therefore, elucidating the process of immunoglobulin production is in great need. Maladaptive immune response in lung tissues is considered implicating in the local auto-antibodies production in patients with IPAH. In this review, we will discuss the specific cell types involved in the lung in situ immune response, the potential auto-antigens, and the contribution of local immunoglobulin production in PAH development, providing a theoretical basis for drug development and precise treatment in patients with PAH.

Central Role of Dendritic Cells in Pulmonary Arterial Hypertension in Human and Mice

The pathogenesis of idiopathic pulmonary arterial hypertension (IPAH) is not fully understood, but evidence is accumulating that immune dysfunction plays a significant role. We previously reported that 31-week-old Tnfaip3^DNGR1-KO mice develop pulmonary hypertension (PH) symptoms. These mice harbor a targeted deletion of the TNFα-induced protein-3 (Tnfaip3) gene, encoding the NF-κB regulatory protein A20, specifically in type I conventional dendritic cells (cDC1s). Here, we studied the involvement of dendritic cells (DCs) in PH in more detail. We found various immune cells, including DCs, in the hearts of Tnfaip3^DNGR1-KO mice, particularly in the right ventricle (RV). Secondly, in young Tnfaip3^DNGR1-KO mice, innate immune activation through airway exposure to toll-like receptor ligands essentially did not result in elevated RV pressures, although we did observe significant RV hypertrophy. Thirdly, PH symptoms in Tnfaip3^DNGR1-KO mice were not enhanced by concomitant mutation of bone morphogenetic protein receptor type 2 (Bmpr2), which is the most affected gene in PAH patients. Finally, in human IPAH lung tissue we found co-localization of DCs and CD8+ T cells, representing the main cell type activated by cDC1s. Taken together, these findings support a unique role of cDC1s in PAH pathogenesis, independent of general immune activation or a mutation in the Bmpr2 gene.

Identification of key genes and immune profile in limited cutaneous systemic sclerosis-associated pulmonary arterial hypertension by bioinformatics analysis

AIMS

Limited cutaneous systemic sclerosis-associated pulmonary arterial hypertension (lcSSc-PAH) is a complex multi-system disease with high morbidity and mortality. The purpose of this study is to identify the hub genes and immune characteristics of limited cutaneous systemic sclerosis (lcSSc) and lcSSc-PAH through bioinformatics.

MAIN METHODS

LcSSc-PAH raw data were obtained from the GEO database (GSE19617). Weighted gene Co-expression Network analysis (WGCNA) was used to evaluate key modules. Then, we performed Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis with R software and verified the diagnostic value of the hub genes. Finally, Immune Cell Abundance Identifier (ImmuCellAI) was used to analyze the immune characteristics of the normal subjects, lcSSc and lcSSc-PAH patients, the results were displayed graphically.

KEY FINDINGS

Enrichment of two important modules by GO and KEGG identified key biological processes and pathways related to pathogen infection and immune function. Three hub genes (BID, IFNGR1, ZAP70) related to immune function were identified. The analysis of immune characteristics showed that the correlation and abundance of immune cells such as inducible regulatory T (iTreg) cells, B cells, macrophages, natural killer (NK) cells, CD8T cells, mucosal-associated invariant T(MAIT) cells and dendritic cells(DCs) were significantly different in the normal subjects, lcSSc and lcSSc-PAH patients.

SIGNIFICANCE

Pathogen infection, changes in the number and function of immune cells, and interactions among immune cells may preliminarily reveal the pathological mechanism of lcSSc-PAH. The hub genes, pathways and immune characteristics identified in this research remains to be further studied.

Inflammation in Pulmonary Arterial Hypertension

Pulmonary artery hypertension (PAH) is a devastating cardiopulmonary disease characterized by vascular remodeling and obliteration of the precapillary pulmonary arterioles. Alterations in the structure and function of pulmonary vessels result in the resistance of blood flow and can progress to right-sided heart failure, causing significant morbidity and mortality. There are several types of PAH, and the disease can be familial or secondary to an underlying medical condition such as a connective tissue disorder or infection. Regardless of the cause, the exact pathophysiology and cellular interactions responsible for disease development and progression are largely unknown.There is significant evidence to suggest altered immune and vascular cells directly participate in disease progression. Inflammation has long been hypothesized to play a vital role in the development of PAH, as an altered or skewed immune response favoring a proinflammatory environment that can lead to the infiltration of cells such as lymphocytes, macrophages, and neutrophils. Current treatment strategies focus on the dilation of partially occluded vessels; however, such techniques have not resulted in an effective strategy to reverse or prevent vascular remodeling. Therefore, current studies in human and animal models have attempted to understand the underlying pathophysiology of pulmonary hypertension (PH), specifically focusing on the inflammatory cascade predisposing patients to disease so that better therapeutic targets can be developed to potentially reverse or prevent disease progression.The purpose of this chapter is to provide a comprehensive review of the expanding literature on the inflammatory process that participates in PH development while highlighting important and current studies in both animal and human models. While our primary focus will be on cells found in the adaptive and innate immune system, we will review all potential causes of PAH, including cells of the endothelium, pulmonary lymphatics, and genetic mutations predisposing patients. In addition, we will discuss current therapeutic options while highlighting potential future treatments and the questions that still remain unanswered.

Cytokines, Chemokines, and Inflammation in Pulmonary Arterial Hypertension

According to the World Symposium Pulmonary Hypertension (WSPH) classification, pulmonary hypertension (PH) is classified into five categories based on etiology. Among them, Group 1 pulmonary arterial hypertension (PAH) disorders are rare but progressive and often, fatal despite multiple approved treatments. Elevated pulmonary arterial pressure in patients with WSPH Group 1 PAH is mainly caused by increased pulmonary vascular resistance (PVR), due primarily to sustained pulmonary vasoconstriction and excessive obliterative pulmonary vascular remodeling. Growing evidence indicates that inflammation plays a critical role in the development of pulmonary vascular remodeling associated with PAH. While the role of auto-immunity is unclear, infiltration of inflammatory cells in and around vascular lesions, including T- and B-cells, dendritic cells, macrophages, and mast cells have been observed in PAH patients. Serum and plasma levels of chemokines, cytokines, and autoantibodies are also increased in PAH patients; some of these circulating molecules are correlated with disease severity and survival. Preclinical experiments have reported a key role of the inflammation in PAH pathophysiology in vivo. Importantly, anti-inflammatory and immunosuppressive agents have further exhibited therapeutic effects. The present chapter reviews published experimental and clinical evidence highlighting the canonical role of inflammation in the pathogenesis of PAH and as a major target for the development of anti-inflammatory therapies in patients with PAH.

DNGR1-Cre-mediated Deletion of Tnfaip3/A20 in Conventional Dendritic Cells Induces Pulmonary Hypertension in Mice

Chronic perivascular inflammation is a prominent feature in the lungs of idiopathic pulmonary arterial hypertension. Although the proportions of conventional dendritic cells (cDCs) and plasmacytoid DCs are increased in idiopathic pulmonary arterial hypertension lungs, it remains unknown whether activated cDCs play a pathogenic role. The Tnfaip3 gene encodes the ubiquitin-binding protein A20, which is a negative regulator of NF-κB, critically involved in DC activation. Targeting of Tnfaip3/A20 in cDCs was achieved by Clec9a (DNGR1)-Cre-mediated excision of the Tnfaip3 gene in Tnfaip3^DNGR1-KO mice. Mice were evaluated for signs of pulmonary hypertension (PH) using right heart catheterization, echocardiography, and measurement of the Fulton index. Inflammation was assessed by immunohistochemistry and flow cytometry. Pulmonary cDCs and monocyte-derived DCs from 31-week-old Tnfaip3^DNGR1-KO mice showed modulated expression of cell surface activation markers compared with Tnfaip3^DNGR1-WT mice. Tnfaip3^DNGR1-KO mice developed elevated right ventricular systolic pressure and right ventricular hypertrophy. The lungs of these mice displayed increased vascular remodeling and perivascular and peribronchial immune cell infiltration resembling tertiary lymphoid organs. Proportions of activated T cells and expression of IL-1β, IL-6, and IL-10 were enhanced in the lungs of Tnfaip3^DNGR1-KO mice. Autoreactive IgA and IgG1 was detected in BAL and autoreactive IgA recognizing pulmonary endothelial antigens was present in the serum of Tnfaip3^DNGR1-KO mice. All signs of PH were ameliorated in Tnfaip3^DNGR1-KO mice by anti-IL-6 antibody treatment. These results indicate that activation of the NF-κB pathway in DCs, through deletion of A20/Tnfaip3, leads to experimental PH with accompanied pulmonary inflammation in an IL-6-dependent fashion.

Perivascular Inflammation in Pulmonary Arterial Hypertension

Perivascular inflammation is a prominent pathologic feature in most animal models of pulmonary hypertension (PH) as well as in pulmonary arterial hypertension (PAH) patients. Accumulating evidence suggests a functional role of perivascular inflammation in the initiation and/or progression of PAH and pulmonary vascular remodeling. High levels of cytokines, chemokines, and inflammatory mediators can be detected in PAH patients and correlate with clinical outcome. Similarly, multiple immune cells, including neutrophils, macrophages, dendritic cells, mast cells, T lymphocytes, and B lymphocytes characteristically accumulate around pulmonary vessels in PAH. Concomitantly, vascular and parenchymal cells including endothelial cells, smooth muscle cells, and fibroblasts change their phenotype, resulting in altered sensitivity to inflammatory triggers and their enhanced capacity to stage inflammatory responses themselves, as well as the active secretion of cytokines and chemokines. The growing recognition of the interaction between inflammatory cells, vascular cells, and inflammatory mediators may provide important clues for the development of novel, safe, and effective immunotargeted therapies in PAH.

Pulmonary Arterial Hypertension and Chronic Thromboembolic Pulmonary Hypertension: An Immunological Perspective

Pulmonary hypertension (PH) is a debilitating progressive disease characterized by increased pulmonary arterial pressures, leading to right ventricular (RV) failure, heart failure and, eventually, death. Based on the underlying conditions, PH patients can be subdivided into the following five groups: (1) pulmonary arterial hypertension (PAH), (2) PH due to left heart disease, (3) PH due to lung disease, (4) chronic thromboembolic PH (CTEPH), and (5) PH with unclear and/or multifactorial mechanisms. Currently, even with PAH-specific drug treatment, prognosis for PAH and CTEPH patients remains poor, with mean five-year survival rates of 57%-59% and 53%-69% for PAH and inoperable CTEPH, respectively. Therefore, more insight into the pathogenesis of PAH and CTEPH is highly needed, so that new therapeutic strategies can be developed. Recent studies have shown increased presence and activation of innate and adaptive immune cells in both PAH and CTEPH patients. Moreover, extensive biomarker research revealed that many inflammatory and immune markers correlate with the hemodynamics and/or prognosis of PAH and CTEPH patients. Increased evidence of the pathological role of immune cells in innate and adaptive immunity has led to many promising pre-clinical interventional studies which, in turn, are leading to innovative clinical trials which are currently being performed. A combination of immunomodulatory therapies might be required besides current treatment based on vasodilatation alone, to establish an effective treatment and prevention of progression for this disease. In this review, we describe the recent progress on our understanding of the involvement of the individual cell types of the immune system in PH. We summarize the accumulating body of evidence for inflammation and immunity in the pathogenesis of PH, as well as the use of inflammatory biomarkers and immunomodulatory therapy in PAH and CTEPH.

Dendritic Cell Subsets and Effector Function in Idiopathic and Connective Tissue Disease-Associated Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a cardiopulmonary disease characterized by an incurable condition of the pulmonary vasculature, leading to increased pulmonary vascular resistance, elevated pulmonary arterial pressure resulting in progressive right ventricular failure and ultimately death. PAH has different underlying causes. In approximately 30–40% of the patients no underlying risk factor or cause can be found, so-called idiopathic PAH (IPAH). Patients with an autoimmune connective tissue disease (CTD) can develop PAH [CTD-associated PAH (CTD-PAH)], suggesting a prominent role of immune cell activation in PAH pathophysiology. This is further supported by the presence of tertiary lymphoid organs (TLOs) near pulmonary blood vessels in IPAH and CTD-PAH. TLOs consist of myeloid cells, like monocytes and dendritic cells (DCs), T-cells, and B-cells. Next to their T-cell activating function, DCs are crucial for the preservation of TLOs. Multiple DC subsets can be found in steady state, such as conventional DCs (cDCs), including type 1 cDCs (cDC1s), and type 2 cDCs (cDC2s), AXL⁺Siglec6⁺ DCs (AS-DCs), and plasmacytoid DCs (pDCs). Under inflammatory conditions monocytes can differentiate into monocyte-derived-DCs (mo-DCs). DC subset distribution and activation status play an important role in the pathobiology of autoimmune diseases and most likely in the development of IPAH and CTD-PAH. DCs can contribute to pathology by activating T-cells (production of pro-inflammatory cytokines) and B-cells (pathogenic antibody secretion). In this review we therefore describe the latest knowledge about DC subset distribution, activation status, and effector functions, and polymorphisms involved in DC function in IPAH and CTD-PAH to gain a better understanding of PAH pathology.

Inflammation in Right Ventricular Failure: Does It Matter?

Right ventricular (RV) failure is a common consequence of acute and chronic RV overload of pressure, such as after pulmonary embolism and pulmonary hypertension. It has been recently realized that symptomatology and survival of patients with pulmonary hypertension are essentially determined by RV function adaptation to increased afterload. Therefore, improvement of RV function and reversal of RV failure are treatment goals. Currently, the pathophysiology and the pathobiology underlying RV failure remain largely unknown. A better understanding of the pathophysiological processes involved in RV failure is needed, as there is no proven treatment for this disease at the moment. The present review aims to summarize the current understanding of the pathogenesis of RV failure, focusing on inflammation. We attempt to formally emphasize the importance of inflammation and associated representative inflammatory molecules and cells in the primum movens and development of RV failure in humans and in experimental models. We present inflammatory biomarkers and immune mediators involved in RV failure. We focus on inflammatory mediators and cells which seem to correlate with the deterioration of RV function and also explain how all these inflammatory mediators and cells might impact RV function adaptation to increased afterload. Finally, we also discuss the evidence on potential beneficial effects of targeted anti-inflammatory agents in the setting of acute and chronic RV failure.

Myeloid-Derived Suppressor Cells and Pulmonary Hypertension

Myeloid–derived suppressor cells (MDSCs) comprised a heterogeneous subset of bone marrow–derived myeloid cells, best studied in cancer research, that are increasingly implicated in the pathogenesis of pulmonary vascular remodeling and the development of pulmonary hypertension. Stem cell transplantation represents one extreme interventional strategy for ablating the myeloid compartment but poses a number of translational challenges. There remains an outstanding need for additional therapeutic targets to impact MDSC function, including the potential to alter interactions with innate and adaptive immune subsets, or alternatively, alter trafficking receptors, metabolic pathways, and transcription factor signaling with readily available and safe drugs. In this review, we summarize the current literature on the role of myeloid cells in the development of pulmonary hypertension, first in pulmonary circulation changes associated with myelodysplastic syndromes, and then by examining intrinsic myeloid cell changes that contribute to disease progression in pulmonary hypertension. We then outline several tractable targets and pathways relevant to pulmonary hypertension via MDSC regulation. Identifying these MDSC-regulated effectors is part of an ongoing effort to impact the field of pulmonary hypertension research through identification of myeloid compartment-specific therapeutic applications in the treatment of pulmonary vasculopathies.

The inflammatory cell landscape in the lungs of patients with idiopathic pulmonary arterial hypertension

Increasing evidence points towards an inflammatory component underlying pulmonary hypertension. However, the conclusive characterisation of multiple inflammatory cell populations in the lung is challenging due to the complexity of marker specificity and tissue inaccessibility. We used an unbiased computational flow cytometry approach to delineate the inflammatory landscape of idiopathic pulmonary arterial hypertension (IPAH) and healthy donor lungs.

Donor and IPAH samples were discriminated clearly using principal component analysis to reduce the multidimensional data obtained from single-cell flow cytometry analysis. In IPAH lungs, the predominant CD45⁺ cell type switched from neutrophils to CD3⁺ T-cells, with increases in CD4⁺, CD8⁺ and γδT-cell subsets. Additionally, diversely activated classical myeloid-derived dendritic cells (CD14⁻HLA-DR⁺CD11c⁺CD1a^+/−) and nonclassical plasmacytoid dendritic cells (pDCs; CD14⁻CD11c⁻CD123⁺HLA-DR⁺), together with mast cells and basophils, were more abundant in IPAH samples. We describe, for the first time, the presence and regulation of two cell types in IPAH, γδT-cells and pDCs, which link innate and adaptive immunity.

With our high-throughput flow cytometry with multidimensional dataset analysis, we have revealed the interactive interplay between multiple inflammatory cells is a crucial part of their integrative network. The identification of γδT-cells and pDCs in this disease potentially provides a missing link between IPAH, autoimmunity and inflammation.

Computational flow cytometry details the complex inflammatory cell landscape in patients with pulmonary hypertensionhttp://ow.ly/rjFZ30g1tew

Immune cells and autoantibodies in pulmonary arterial hypertension

Analyses of immunity in pulmonary arterial hypertension (PAH) support the notion that maladaptation of the immune response exists. Altered immunity is an increasingly recognized feature of PAH. Indeed, a delicate balance between immunity and tolerance exists and any disturbance may result in chronic inflammation or autoimmunity. This is suggested by infiltration of various immune cells (e.g. macrophages, T and B lymphocytes) in remodeled pulmonary vessels. In addition, several types of autoantibodies directed against antinuclear antigens, endothelial cells (ECs) and fibroblasts have been found in idiopathic and systemic sclerosis-associated PAH. These autoantibodies may play an important role in EC apoptosis and in the expression of cell adhesion molecules. This review article provides an overview of immunity pathways highlighting their potential roles in pulmonary vascular remodeling in PAH and the possibility of future targeted therapy.

Microarray profiling of long non-coding RNAs associated with idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is a fatal disease with a poor prognosis and the molecular pathways underlying the pathogenesis of IPAH are not fully understood. In the present study, the long non-coding RNA (lncRNA) and mRNA expression profiles of lymphocytes obtained from 12 IPAH patients and 12 healthy controls were analyzed using Arraystar Human lncRNA Microarray v2.0, and their roles in the pathogenesis of IPAH were characterized using comprehensive bioinformatic tools. A total of 2,511 lncRNAs (2,004 upregulated and 507 downregulated) and 1,169 mRNAs (609 upregulated and 560 downregulated) were aberrantly expressed in IPAH patients with a fold-change of >2.0. Gene ontology analysis indicated that the coexpressed lncRNAs and mRNAs were involved in the process of translation, while pathway analysis indicated that the coexpressed RNAs were enriched during the process of oxidative phosphorylation and in the ribosome. It was concluded that dysregulated lncRNAs are potentially associated with IPAH, and aberrant lncRNA expression in blood cells may serve as a diagnostic marker of IPAH.

Nuclear factor κ-B is activated in the pulmonary vessels of patients with end-stage idiopathic pulmonary arterial hypertension

OBJECTIVES

To assess activation of the inflammatory transcription factor NF-kappa B (NF-κB) in human idiopathic pulmonary arterial hypertension (PAH).

BACKGROUND

Idiopathic PAH is a severe progressive disease characterized by pulmonary vascular remodeling and excessive proliferation of vascular cells. Increasing evidence indicates that inflammation is important in disease pathophysiology.

METHODS

NF-κB-p65 and CD68, CD20 and CD45 were measured by immunohistochemistry and confocal microscopy on lung specimens from patients with idiopathic PAH (n = 12) and controls undergoing lung surgery (n = 14). Clinical data were recorded for all patients including invasive pulmonary hemodynamics for the PAH patients. Immunohistochemical images were analyzed by blinded observers to include standard pulmonary vascular morphometry; absolute macrophage counts/mm(2) and p65-positivity (p65+) using composite images and image-analysis software; and cytoplasmic:nuclear p65+ of individual pulmonary arterial endothelial and smooth muscle cells (PASMC) in 10-20 pulmonary arteries or arterioles per subject. The expression of ET-1 and CCL5 (RANTES) in whole lung was determined by RT-qPCR.

RESULTS

Macrophage numbers were increased in idiopathic PAH versus controls (49.0±4.5 vs. 7.95±1.9 macrophages/100 mm(2), p<0.0001): these macrophages demonstrated more nuclear p65+ than in macrophages from controls (16.9±2.49 vs. 3.5±1.25%, p<0.001). An increase in p65+ was also seen in perivascular lymphocytes in patients with PAH. Furthermore, NF-κB activation was increased in pulmonary arterial endothelial cells (62.3±2.9 vs. 14.4±3.8, p<0.0001) and PASMC (22.6±2.3 vs. 11.2±2.0, p<0.001) in patients with PAH versus controls, with similar findings in arterioles. Gene expression of both ET-1 mRNA ((0.213±0.069 vs. 1.06±0.23, p<0.01) and CCL5 (RANTES) (0.16±0.045 vs. 0.26±0.039, p<0.05) was increased in whole lung homogenates from patients with PAH.

CONCLUSIONS

NF-κB is activated in pulmonary macrophages, lymphocytes, endothelial and PASMC in patients with end-stage idiopathic PAH. Future research should determine whether NF-κB activation is a driver or bystander of pulmonary vascular inflammation and if the former, its potential role as a therapeutic target.

Circulating myeloid-derived suppressor cells are increased and activated in pulmonary hypertension

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) are increased in inflammatory and autoimmune disorders and orchestrate immune cell responses therein. Pulmonary hypertension (PH) is associated with inflammation, autoimmunity, and lung vascular remodeling. Immature myeloid cells are found in the lungs of humans and animals with PH, and we hypothesized that they would be increased in the blood of patients with PH compared with control subjects.

METHODS

Twenty-six children with PH and 10 undergoing cardiac catheterization for arrhythmia ablation were studied. Five milliliters of fresh blood were analyzed using flow cytometry. Results were confirmed using magnetic bead sorting and immunofluorescence, while quantitative polymerase chain reaction and intracellular urea concentration assays were used as measures of MDSC arginase-1 activation.

RESULTS

Flow cytometry demonstrated enrichment of circulating MDSCs among patients with PH (n = 26; mean, 0.271 × 10(6) cells/mL ± 0.17; 1.86% of CD45(+) population ± 1.51) compared with control subjects (n = 10; mean, 0.176 × 10(6) cells/mL ± 0.05; 0.57% of CD45(+) population ± 0.29; P < .05). Higher numbers of circulating MDSCs correlated to increasing mean pulmonary artery pressure (r = 0.510, P < .05). Among patients with PH, female patients had a twofold increase in MDSCs compared with male patients. Immunofluorescence analysis confirmed the results of flow cytometry. Quantitative reverse transcription polymerase chain reaction assay results for arginase-1 and measurement of intracellular urea concentration revealed increased activity of MDSCs from patients with PH compared with control subjects.

CONCLUSIONS

Circulating activated MDSCs are significantly increased in children with PH compared with control subjects. Further investigation of these cells is warranted, and we speculate that they might play significant immunomodulatory roles in the disease pathogenesis of PH.

Lack of CCR7 induces pulmonary hypertension involving perivascular leukocyte infiltration and inflammation

The chemokine receptor CCR7 regulates lymphocyte trafficking, and CCR7 deficiency induces infiltration of T and B cells adjacent to vessels in mouse lungs. Perivascular infiltration of T and B cells has also been found in human pulmonary arterial hypertension, and downregulation of the CCR7 receptor in circulating leukocytes of such patients has been observed. To investigate whether changes in the CCR7 system contribute to the pathogenesis of pulmonary hypertension, we utilized mice deficient of the CCR7 receptor. The cardiopulmonary and inflammatory responses of CCR7 depletion were evaluated in CCR7-deficient and wild-type mice. Measurements of cytokines upregulated in the animal model were also performed in patients with pulmonary hypertension and controls and in vascular smooth muscle cells. We found that mice lacking CCR7 had increased right ventricular systolic pressure, reduced pulmonary artery acceleration time, increased right ventricular/tibial length ratio, Rho kinase-mediated pulmonary vasoconstriction, and increased muscularization of distal arteries, indicating pulmonary hypertension. These mice also showed increased perivascular infiltration of leukocytes, consisting mainly of T and B cells, and increased mRNA levels of the inflammatory cytokines interleukin-12 and CX3CL1 within pulmonary tissue. Increased serum levels of interleukin-12 and CX3CL1 were also observed in patients with pulmonary hypertension, particularly in those with pulmonary hypertension associated with connective tissue disorder. In smooth muscle cells, interleukin-12 induced secretion of the angiogenic cytokine interleukin-8. We conclude that these results suggest a role for CCR7 in the development of pulmonary arterial hypertension, at least in some subgroups, possibly via pulmonary infiltration of lymphocytes and secretion of interleukin-12 and CX3CL1.