Therapeutic ACPA inhibits NET formation: a potential therapy for neutrophil-mediated inflammatory diseases

Targeting programmed cell death in inflammatory bowel disease through natural products: New insights from molecular mechanisms to targeted therapies

Inflammatory bowel disease (IBD) is an autoimmune disorder primarily characterized by intestinal inflammation and recurrent ulceration, leading to a compromised intestinal barrier and inflammatory infiltration. This disorder's pathogenesis is mainly attributed to extensive damage or death of intestinal epithelial cells, along with abnormal activation or impaired death regulation of immune cells and the release of various inflammatory factors, which contribute to the inflammatory environment in the intestines. Thus, maintaining intestinal homeostasis hinges on balancing the survival and functionality of various cell types. Programmed cell death (PCD) pathways, including apoptosis, pyroptosis, autophagy, ferroptosis, necroptosis, and neutrophil extracellular traps, are integral in the pathogenesis of IBD by mediating the death of intestinal epithelial and immune cells. Natural products derived from plants, fruits, and vegetables have shown potential in regulating PCD, offering preventive and therapeutic avenues for IBD. This article reviews the role of natural products in IBD treatment by focusing on targeting PCD pathways, opening new avenues for clinical IBD management.

Neutrophil Extracellular Traps Are Widely Distributed Across Lesional and Perilesional Hidradenitis Suppurativa Skin, and Elevated Serum NET Markers Associate With Moderate to Severe HS Disease

BACKGROUND

Neutrophils are scarce in healthy skin but infiltrate lesions of hidradenitis suppurativa (HS) patients. Activated neutrophils release proinflammatory neutrophil extracellular traps (NETs), which have been implicated in the pathophysiology of HS. This study aimed to describe the distribution of NETs relative to the features of HS skin lesions and reveal whether serum NET markers were elevated in association with disease activity.

METHODS

Immunohistochemistry assessed the distribution of the key NET component citrullinated histone H3 (CitH3) in lesional, perilesional, and unaffected HS skin. Several markers of NETs (nucleosomes, calprotectin, and CitH3) were quantified in HS serum with ELISA.

RESULTS

HS lesional skin biopsies showed increased CitH3-positive staining compared to unaffected skin. This signal was widely distributed across both lesional and perilesional regions of HS skin and was associated with HS structures such as the lining of epithelialized skin tunnels. Moreover, several NET-associated markers were elevated in the serum of HS patients compared to healthy volunteers and correlated with each other. Finally, serum NET markers showed significant elevation in patients with moderate to severe disease activity based on IHS-4 scores, compared to those with no or mild activity.

CONCLUSIONS

Elevated NET markers are widely distributed in HS skin and serum. These data indicate that NET-associated markers in serum are candidate biomarkers for HS disease severity. The results confirm the rationale for anti-inflammatory therapy targeting NETs in HS.

Complex regulation of cardiac fibrosis: insights from immune cells and signaling pathways

Cardiac fibrosis is a physiological process that involves the formation of scar tissue in the heart in response to injury or damage. This process is initially a protective measure characterized by enhanced fibroblasts, which are responsible for producing extracellular matrix proteins that provide structural support to the heart. However, when fibrosis becomes excessive, it can lead to adverse outcomes, including increasing tissue stiffness and impaired cardiac function, which can ultimately result in heart failure with a poor prognosis. While fibroblasts are the primary cells involved in cardiac fibrosis, immune cells have also been found to play a vital role in its progression. Recent research has shown that immune cells exert multifaceted effects besides regulation of inflammatory response. Advanced research techniques such as single-cell sequencing and multiomics have provided insights into the specific subsets of immune cells involved in fibrosis and the complex regulation of the process. Targeted immunotherapy against fibrosis is gaining traction as a potential treatment option, but it is still unclear how immune cells achieve this regulation and whether distinct subsets are involved in different roles. To better understand the role of immune cells in cardiac fibrosis, it is essential to examine the classical signaling pathways that are closely related to fibrosis formation. We have also focused on the unique properties of diverse immune cells in cardiac fibrosis and their specific intercommunications. Therefore, this review will delve into the plasticity and heterogeneity of immune cells and their specific roles in cardiac fibrosis, which propose insights to facilitate the development of anti-fibrosis therapeutic strategies.

Insights into the complexities of Citrullination: From immune regulation to autoimmune disease

Citrullination, a post-translational modification that changes arginine to citrulline in proteins, is vital for immune response modulation and cell signaling. Catalyzed by peptidyl arginine deiminases (PADs), citrullination is linked to various diseases, particularly autoimmune disorders like rheumatoid arthritis (RA). Citrullinated proteins can trigger the production of anti-citrullinated protein antibodies (ACPAs), included in RA classification criteria. The immune response to citrullination involves both innate and adaptive immunity, affecting monocytes/macrophages, neutrophils, dendritic cells, natural killer cells, B cells, and T cells. Citrullination contributes to disease development in RA and other conditions such as multiple sclerosis, sepsis, and cancer. Therapeutic strategies targeting citrullination and its effects are being explored, including B cell depletion therapies, T cell-directed approaches, PAD inhibitors, and citrullinated peptide-based vaccines. Understanding the interplay between citrullination and the immune system may lead to novel diagnostic tools and targeted therapies for autoimmune diseases and beyond.

Inhibition of EETosis with an anti-citrullinated histone antibody: a novel therapeutic approach for eosinophilic inflammatory disorders

Eosinophils are a subset of granulocytes that protect the host against fungal and parasitic infection through secretion of their granular contents. In response to specific stimuli, eosinophils also undergo a type of lytic cell death, referred to as eosinophil extracellular trap (EET)-associated cell death (EETosis), where histone citrullination facilitates chromatin decondensation, cell rupture and release of pro-inflammatory, decondensed chromatin into the extracellular environment as EETs. In this study, we show the abundant presence of eosinophils and citrullinated histones in nasal polyp tissue of patients with eosinophilic chronic rhinosinusitis (ECRS). Using live imaging microscopy on purified human eosinophils, we demonstrate that physiologically relevant stimuli induce release of citrullinated EETs and the marker of eosinophil activation galectin-10. While the kinetics of release of EETs and galectin-10 are similar, inhibitors of citrullination block EETosis in a dose dependent manner but fail to inhibit galectin-10 release. The importance of citrullination is further exemplified with CIT-013, a monoclonal antibody specific for citrullinated histones H2A and H4. CIT-013 potently inhibits release of EETs (half-maximal inhibitory concentration of 2.5 nM) without inhibiting other eosinophil functions such as degranulation, adhesion, superoxide production and induction of chemokine expression. Together, this study provides new insights into the requirement of protein arginine deiminase 4 (PAD4) for EETosis, differentiates requirements of EETosis from galectin-10 release, and identifies a novel therapeutic approach for EETosis inhibition by targeting citrullinated histones in eosinophil-driven diseases such as ECRS.

Research progress on the relationship between neutrophil extra-cellular traps and autogenous arteriovenous fistula thrombosis

Autogenous arteriovenous fistula (AVF) is the preferred vascular access for long-term hemodialysis, and thrombosis is one of the most common complications. In recent years, it has been found that neutrophil extra-cellular traps (NETs) play an important role in thrombosis. NETs are a kind of network structure with DNA as a skeleton and intercalated with a variety of granule proteins, proteolytic enzymes, antimicrobial peptides and histone proteins, which are released into the extracellular space by neutrophils after stimulation. In this paper, the NETs in the role of AVF thrombus formation and NETs in the value of prevention and cure of AVF thrombus complications were reviewed.

Neutrophil Extracellular Traps (NETs) as a Potential Target for Anti-Aging: Role of Therapeutic Apheresis

Neutrophil extracellular traps (NETs) are large structures composed of chromatin, histones and granule-derived proteins released extracellularly by neutrophils. They are generally considered to be a part of the antimicrobial defense strategy, preventing the dissemination of pathogens. However, overproduction of NETs or their ineffective clearance can drive various pathologies, many of which are associated with advanced age and involve uncontrolled inflammation, oxidative, cardiovascular and neurodegenerative stress as underlying mechanisms. Targeting NETs in the elderly as an anti-aging therapy seems to be a very attractive therapeutic approach. Therapeutic apheresis with a specific filter to remove NETs could be a promising strategy worth considering.

Large-scale multicenter study reveals anticitrullinated SR-A peptide antibody as a biomarker and exacerbator for rheumatoid arthritis

Current diagnosis and treatment of rheumatoid arthritis (RA) is still challenging. More than one-third of patients with RA could not be accurately diagnosed because of lacking biomarkers. Our recent study reported that scavenger receptor-A (SR-A) is a biomarker for RA, especially for anticyclic citrullinated peptide antibody (anti-CCP)-negative RA. Here, we further identified the B cell autoantigenic epitopes of SR-A. By a large-scale multicenter study including one training and three validation cohorts of 1954 participants, we showed that anticitrullinated SR-A peptide antibody (anti-CSP) was exclusively elevated in RA as a biomarker, particularly useful for seronegative RA. Combination of anti-CSP with anti-CCP demonstrated superior diagnostic value for RA, with sensitivity of 84.83% and specificity of 92.43%. Moreover, RA anti-CSP revealed distinct glycosylation patterns, capable of provoking inflammation in cartilage organoids and exacerbating disease progression in experimental arthritis. Together, these data identify anti-CSP as an RA autoantibody clinically applicable and actively involved in disease pathogenesis.

Neutrophil extracellular traps and oxidative stress in systemic lupus erythematosus patients with and without renal involvement

OBJECTIVES

To investigate the levels of plasma neutrophil extracellular traps (NETs) and free thiols, the latter reflecting systemic oxidative stress (OS), and to explore the relationship between NETs and OS in quiescent systemic lupus erythematosus (SLE) patients with and without renal involvement.

METHODS

Plasma levels of NETs and free thiols were measured cross-sectionally in 100 SLE patients with low disease activity (SLEDAI < 5), of whom 73 patients had no renal involvement (non-LN) and 27 patients had lupus nephritis (LN). Additionally, 22 healthy controls (HCs) were included. NETs were measured using a myeloperoxidase-DNA complex ELISA and free thiols were measured using a thiol assay kit.

RESULTS

NETs levels were significantly higher in both non-LN and LN patients compared to HCs (p < 0.001, p = 0.013), with no difference between the two patient groups (p = 0.799). Free thiol levels were not significantly different between groups. Interestingly, NETs were negatively correlated with free thiols in all 100 SLE patients (rho = -0.32) and non-LN patients (rho = -0.38), but not in LN patients. Levels of free thiols were significantly lower in subgroups of patients with estimated glomerular filtration rate (eGFR) < 60, serum creatinine (sCr) ≥ 90, C reactive protein (CRP) levels ≥ 5 and body mass index (BMI) ≥ 30. In multivariable regression, disease duration, NETs levels, and eGFR were independently associated with free thiol levels.

CONCLUSIONS

Levels of NETs were increased in quiescent SLE patients. Although free thiol levels did not differ among the groups. The levels of NETs and free thiols were independently associated in SLE patients, suggesting a potential role of OS in NETs formation. Therefore, reducing OS might be an additional therapeutic target for SLE treatment.

Attenuation of neutrophil adhesion and formation of neutrophil extracellular traps by pooled human immune globulins

Introduction

This study investigated the efficacy of pooled human immune globulins (Flebogamma® DIF) to combat the formation of neutrophil extracellular traps (NETs) and NETosis, along with neutrophil adhesion to corneal epithelial cells in response to dry eye disease relevant stimuli.

Methods

Human neutrophils were isolated by bead-based immunomagnetic depletion of non-target cells from human whole blood. NETosis was induced using phorbol 12-myristate 13-acetate (PMA) or anti-citrullinated histone 4 R3 antibody (H4R3 ACPA). Extracellular DNA was used as a surrogate biomarker of NETosis, and it was quantified using a 96-well, plate reader-based fluorescent assay and by confocal microscopy in 8-well chambers using the DNA dye, SYTOXTM Green. Neutrophils were labeled with calcein-AM and adhesion to human corneal epithelial cells was measured. The efficacy of a dose-range of pooled human immune globulin (Flebogamma® DIF, 0.01%-5%) was tested in all assays.

Results

Pooled human immune globulins (Flebogamma® DIF) dose-dependently inhibited both PMA and H4R3 ACPA induced NETosis, with concentrations ≥2.5% fully preventing release of extracellular DNA over a 2-16 h time period. Similarly, Flebogamma® 5% DIF prevented NETosis against PMA (20 nM) and a dose range (0.1-10 μg/mL) of H4R3 ACPA. Both PMA and H4R3 ACPA increased adhesion of neutrophils to corneal epithelial cells by 20% and 5%, respectively. Flebogamma® DIF treatment resulted in a dose-dependent reduction of neutrophil adhesion, with Flebogamma® 5% DIF reducing adhesion to baseline levels.

Discussion

These findings show the dose-dependent efficacy of pooled human immune globulins, specifically Flebogamma® DIF against experimentally and pathologically induced NETosis and neutrophil adhesion to corneal epithelial cells, in vitro. The results from this study support the continued clinical development of Flebogamma® 5% DIF as a novel and efficacious treatment for the signs and symptoms of dry eye disease.

Extracellular vesicle autoantibodies

Autoantibodies are immunoglobulin proteins produced by autoreactive B cells responding to self-antigens. Extracellular vesicles (EVs) are membranous structures released by almost all types of cells and extensively distributed in various biological fluids. Studies have indicated that EVs loaded with self-antigens not only play important roles in antigen presentation and autoantibody production but can also form functional immune complexes with autoantibodies (termed EV autoantibodies). While numerous papers have summarized the production and function of pathogenic autoantibodies in diseases, especially autoimmune diseases, reviews on EV autoantibodies are rare. In this review, we outline the existing knowledge about EVs, autoantibodies, and EV antigens, highlighting the formation of EV autoantibodies and their functions in autoimmune diseases and cancers. In conclusion, EV autoantibodies may be involved in the occurrence of disease(s) and also serve as potential non-invasive markers that could help in the diagnosis and/or prognosis of disease. Additional studies designed to define in more detail the molecular characteristics of EV autoantibodies and their contribution to disease are recommended.

Neutrophil extracellular traps: a catalyst for atherosclerosis

Neutrophil extracellular traps (NETs) are network-like structures released by activated neutrophils. They consist mainly of double-stranded DNA, histones, and neutrophil granule proteins. Continuous release of NETs in response to external stimuli leads to activation of surrounding platelets and monocytes/macrophages, resulting in damage to endothelial cells (EC) and vascular smooth muscle cells (VSMC). Some clinical trials have demonstrated the association between NETs and the severity and prognosis of atherosclerosis. Furthermore, experimental findings have shed light on the molecular mechanisms by which NETs contribute to atherogenesis. NETs play a significant role in the formation of atherosclerotic plaques. This review focuses on recent advancements in the understanding of the relationship between NETs and atherosclerosis. It explores various aspects, including the formation of NETs in atherosclerosis, clinical trials investigating NET-induced atherosclerosis, the mechanisms by which NETs promote atherogenesis, and the translational implications of NETs. Ultimately, we aim to propose new research directions for the diagnosis and treatment of atherosclerosis.

Phillyrin inhibits oxidative stress and neutrophil extracellular trap formation through the KEAP1/NRF2 pathway in gouty arthritis

Gouty arthritis (GA) is an inflammatory disorder characterized by deposition of monosodium urate (MSU) crystal in joints. Phillyrin, a natural compound with anti-inflammatory properties, shows promise in mitigating inflammatory responses. This study investigates the therapeutic potential of phillyrin in GA and explores its mechanisms of action. GA was induced in mice via intraarticular MSU injection, and joint inflammation, inflammatory cell infiltration, and their level in serum/tissue were assessed. Key proteins in the NF-κB and NLRP3 pathways were examined using western blot analysis. The impact of phillyrin on oxidative stress, neutrophil extracellular trap (NET) formation, and neutrophil accumulation was evaluated by measuring CD11b + Ly6G + cells, MPO, CitH3, extracellular DNA ratio, and oxidative stress markers. In vitro studies assessed the effects of phillyrin on oxidative stress, cell viability, cytokine production, and NET formation in MSU-treated neutrophils. The KEAP1/NRF2 pathway's role was analyzed using ML385, an NRF2 inhibitor. Phillyrin significantly reversed MSU-induced ankle swelling and inflammatory cell infiltration in joint tissues. It suppressed pro-inflammatory cytokines and proteins in the NF-κB and NLRP3 pathways. Phillyrin reduced neutrophil infiltration, evidenced by lower MPO activity and NET formation, marked by reduced CitH3 expression. In vitro, phillyrin inhibited inflammatory marker expression and NET formation without affecting cell viability. It also restored antioxidant enzyme levels and reduced ROS production, regulating the KEAP1/NRF2 pathway, enhancing NRF2 expression and stability. These effects were reversed by NRF2 inhibition with ML385. Phillyrin alleviates GA by reducing joint inflammation, inhibiting NET formation, and suppressing oxidative stress through NRF2 modulation.

Unraveling the intricacies of neutrophil extracellular traps in inflammatory bowel disease: Pathways, biomarkers, and promising therapies

The development of inflammatory bowel disease (IBD), including ulcerative colitis and Crohn's disease, involves various factors and is characterized by persistent inflammation of the mucosal lining. However, the role of neutrophils in this process remains controversial. Neutrophil extracellular traps (NETs), which consist of chromatin, antimicrobial proteins, and oxidative enzymes, are released by neutrophils to trap pathogens. They are also involved in various immune-mediated and vascular diseases. NETs act as a vital defense mechanisms at the gut-mucosal interface and are frequently exposed to bacterial, viral, and fungal threats. However, they can also contribute to inflammation and worsen imbalances in the gut bacteria. Recent studies have suggested that NETs have a significant impact on IBD development. Previous studies have shown increased levels of NETs in tissue and blood samples from patients with IBD, as well as in experimental colitis mouse models. Therefore, this review discusses how NETs are formed and their role in the pathophysiology of IBD. It discusses how NETs may lead to tissue damage and contribute to IBD-associated complications. Moreover, non-invasive biomarkers are needed to replace invasive procedures such as endoscopy to better evaluate the disease status. Given the crucial role of NETs in IBD progression, this review focuses on potential NET biomarkers that can help predict the evolution of IBD. Furthermore, this review identifies potential therapeutic targets for regulating NET production, which could expand the range of available treatment options for IBD.

Pathogenic role of anti-nuclear autoantibodies in systemic sclerosis: Insights from other rheumatic diseases

Systemic sclerosis (SSc) is a severe autoimmune disease characterized by vasculopathy, fibrosis, and dysregulated immunity, with hallmark autoantibodies targeting nuclear antigens such as centromere protein (ACA) and topoisomerase I (ATA). These autoantibodies are highly prevalent and disease-specific, rarely coexisting, thus serving as crucial biomarkers for SSc diagnosis. Despite their diagnostic value, their roles in SSc pathogenesis remain unclear. This review summarizes current literature on ACA and ATA in SSc, comparing them to autoantibodies in other rheumatic diseases to elucidate their potential pathogenic roles. Similarities are drawn with anti-citrullinated protein antibodies (ACPA) in rheumatoid arthritis, particularly regarding disease specificity and minimal pathogenic impact of antigen binding. In addition, differences between ANA and ACPA in therapeutic responses and Fab glycosylation patterns are reviewed. While ACA and ATA are valuable for disease stratification and monitoring activity, understanding their origins and the associated B cell responses is critical for advancing therapeutic strategies for SSc.

Neutrophil extracellular traps and cardiovascular disease: Associations and potential therapeutic approaches

Cardiovascular disease (CVD) is a significant global health concern, ranking among the top five causes of disability-adjusted life-years (DALY) in 190 countries and territories. Neutrophils, key players in the innate immune system, combat infections by releasing neutrophil extracellular traps (NETs) composed of DNA, histones, elastase, myeloperoxidase, and antimicrobial peptides. This paper explores the relationship between NETs and cardiovascular diseases, focusing on conditions such as heart failure, pulmonary hypertension, atrial fibrillation, and ischemia-reperfusion injury. Particularly, it delves into the impact of NETs on atrial fibrillation and pulmonary hypertension, as well as the role of myeloperoxidase (MPO) and neutrophil elastase (NE) in these diseases. Furthermore, the potential of targeting NETs for the treatment of cardiovascular diseases is discussed.

Peptidyl arginine deiminase-4 inhibitor ameliorates pulmonary fibrosis through positive regulation of developmental endothelial locus-1

Recurring lung injury, chronic inflammation, aberrant tissue repair and impaired tissue remodelling contribute to the pathogenesis of pulmonary fibrosis (PF). Neutrophil extracellular traps (NETs) are released by activated neutrophils to trap, immobilise and kill invading pathogen and is facilitated by peptidyl arginine deiminase-4 (PAD-4). Dysregulated NETs release and abnormal PAD-4 activation plays a crucial role in activating pro-fibrotic events in PF. Developmental endothelial locus-1 (Del-1), expressed by the endothelial cells of lungs and brain acts as an endogenous inhibitor of inflammation and fibrosis. We have hypothesised that PAD-4 inhibitor exerts anti-inflammatory and anti-fibrotic effects in mice model of PF. We have also hypothesised by PAD-4 regulated the transcription of Del-1 through co-repression and its inhibition potentiates anti-fibrotic effects of Del-1. In our study, the PAD-4 inhibitor chloro-amidine (CLA) demonstrated anti-NETotic and anti-inflammatory effects in vitro in differentiated HL-60 cells. In a bleomycin-induced PF mice model, CLA administration in two doses (3 mg/kg, I.P and 10 mg/kg, I.P) improved lung function, normalized bronchoalveolar lavage fluid parameters, and attenuated fibrotic events, including markers of extracellular matrix and epithelial-mesenchymal transition. Histological analyses confirmed the restoration of lung architecture and collagen deposition with CLA treatment. ELISA, IHC, IF, RT-PCR, and immunoblot analysis supported the anti-NETotic effects of CLA. Furthermore, BLM-induced PF reduced Del-1 and p53 expression, which was normalized by CLA treatment. These findings suggest that inhibition of PAD-4 results in amelioration of PF in animal model and may involve modulation of Del-1 and p53 pathways, warranting further investigation.

Neutrophils-biology and diversity

Neutrophils, the most abundant white blood cells in the human circulation, play crucial roles in various diseases, including kidney disease. Traditionally viewed as short-lived pro-inflammatory phagocytes that release reactive oxygen species, cytokines and neutrophil extracellular traps, recent studies have revealed their complexity and heterogeneity, thereby challenging this perception. Neutrophils are now recognized as transcriptionally active cells capable of proliferation and reverse migration, displaying phenotypic and functional heterogeneity. They respond to a wide range of signals and deploy various cargo to influence the activity of other cells in the circulation and in tissues. They can regulate the behavior of multiple immune cell types, exhibit innate immune memory, and contribute to both acute and chronic inflammatory responses while also promoting inflammation resolution in a context-dependent manner. Here, we explore the origin and heterogeneity of neutrophils, their functional diversity, and the cues that regulate their effector functions. We also examine their emerging role in infectious and non-infectious diseases with a particular emphasis on kidney disease. Understanding the complex behavior of neutrophils during tissue injury and inflammation may provide novel insights, thereby paving the way for potential therapeutic strategies to manage acute and chronic conditions. By deciphering their multifaceted role, targeted interventions can be developed to address the intricacies of neutrophil-mediated immune responses and improve disease outcomes.

The emerging role of neutrophil extracellular traps in the progression of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease with a complex etiology. Neutrophil extracellular traps (NETs are NETwork protein structures activated by neutrophils to induce the cleavage and release of DNA-protein complexes). Current studies have shown the critical involvement of NETs in the progression of autoimmune diseases, Neutrophils mostly gather in the inflammatory sites of patients and participate in the pathogenesis of autoimmune diseases in various ways. NETs, as the activated state of neutrophils, have attracted much attention in immune diseases. Many molecules released in NETs are targeted autoantigens in autoimmune diseases, such as histones, citrulline peptides, and myeloperoxidase. All of these suggest that NETs have a direct causal relationship between the production of autoantigens and autoimmune diseases. For RA in particular, as a disorder of the innate and adaptive immune response, the pathogenesis of RA is inseparable from the generation of RA. In this article, we investigate the emerging role of NETs in the pathogenesis of RA and suggest that NETs may be an important target for the treatment of inflammatory autoimmune diseases.

Emerging therapeutic strategies targeting extracellular histones for critical and inflammatory diseases: an updated narrative review

Extracellular histones are crucial damage-associated molecular patterns involved in the development and progression of multiple critical and inflammatory diseases, such as sepsis, pancreatitis, trauma, acute liver failure, acute respiratory distress syndrome, vasculitis and arthritis. During the past decade, the physiopathologic mechanisms of histone-mediated hyperinflammation, endothelial dysfunction, coagulation activation, neuroimmune injury and organ dysfunction in diseases have been systematically elucidated. Emerging preclinical evidence further shows that anti-histone strategies with either their neutralizers (heparin, heparinoids, nature plasma proteins, small anion molecules and nanomedicines, etc.) or extracorporeal blood purification techniques can significantly alleviate histone-induced deleterious effects, and thus improve the outcomes of histone-related critical and inflammatory animal models. However, a systemic evaluation of the efficacy and safety of these histone-targeting therapeutic strategies is currently lacking. In this review, we first update our latest understanding of the underlying molecular mechanisms of histone-induced hyperinflammation, endothelial dysfunction, coagulopathy, and organ dysfunction. Then, we summarize the latest advances in histone-targeting therapy strategies with heparin, anti-histone antibodies, histone-binding proteins or molecules, and histone-affinity hemoadsorption in pre-clinical studies. Finally, challenges and future perspectives for improving the clinical translation of histone-targeting therapeutic strategies are also discussed to promote better management of patients with histone-related diseases.

The role of anti-citrullinated protein antibody in pathogenesis of RA

Rheumatoid arthritis (RA) is a common autoimmune rheumatic disease that causes chronic synovitis, bone erosion, and joint destruction. The autoantigens in RA include a wide array of posttranslational modified proteins, such as citrullinated proteins catalyzed by peptidyl arginine deiminase4a. Pathogenic anti-citrullinated protein antibodies (ACPAs) directed against a variety of citrullinated epitopes are abundant both in plasma and synovial fluid of RA patients. ACPAs play an important role in the onset and progression of RA. Intensive and extensive studies are being conducted to unveil the mechanisms of RA pathogenesis and evaluate the efficacy of some investigative drugs. In this review, we focus on the formation and pathogenic function of ACPAs.

The peculiar features, diversity and impact of citrulline-reactive autoantibodies

Since entering the stage 25 years ago as a highly specific serological biomarker for rheumatoid arthritis, anti-citrullinated protein antibodies (ACPAs) have been a topic of extensive research. This hallmark B cell response arises years before disease onset, displays interpatient autoantigen variability, and is associated with poor clinical outcomes. Technological and scientific advances have revealed broad clonal diversity and intriguing features including high levels of somatic hypermutation, variable-domain N-linked glycosylation, hapten-like peptide interactions, and clone-specific multireactivity to citrullinated, carbamylated and acetylated epitopes. ACPAs have been found in different isotypes and subclasses, in both circulation and tissue, and are secreted by both plasmablasts and long-lived plasma cells. Notably, although some disease-promoting features have been reported, results now demonstrate that certain monoclonal ACPAs therapeutically block arthritis and inflammation in mouse models. A wealth of functional studies using patient-derived polyclonal and monoclonal antibodies have provided evidence for pathogenic and protective effects of ACPAs in the context of arthritis. To understand the roles of ACPAs, one needs to consider their immunological properties by incorporating different facets such as rheumatoid arthritis B cell biology, environmental triggers and chronic antigen exposure. The emerging picture points to a complex role of citrulline-reactive autoantibodies, in which the diversity and dynamics of antibody clones could determine clinical progression and manifestations.

Targeting extranuclear histones to alleviate acute and chronic inflammation

Extracellular histones instigate an inflammatory triad - centered on cytotoxicity, immune cell stimulation, and coagulation - ultimately shaping the dynamics and outcome of various inflammatory pathologies. Given the virtual absence of beneficial functions of histones in the extracellular space, in recent years a number of interference strategies have emerged. In this review we summarize pathogenic functions of extracellular histones and highlight current developments of therapeutic interference. Finally, we elaborate on the current status of preclinical attempts to interfere with extracellular histones in the context of a focus on sepsis and cardiovascular diseases, both of which are leading causes of mortality worldwide.

Immune response to post-translationally modified proteins in rheumatoid arthritis: what makes it special?

Rheumatoid arthritis (RA) exhibits common characteristics with numerous other autoimmune diseases, including the presence of susceptibility genes and the presence of disease-specific autoantibodies. Anti-citrullinated protein antibodies (ACPA) are the hallmarking autoantibodies in RA and the anti-citrullinated protein immune response has been implicated in disease pathogenesis. Insight into the immunological pathways leading to anti-citrullinated protein immunity will not only aid understanding of RA pathogenesis, but may also contribute to elucidation of similar mechanisms in other autoantibody-positive autoimmune diseases. Similarly, lessons learnt in other human autoimmune diseases might be relevant to understand potential drivers of RA. In this review, we will summarise several novel insights into the biology of the anti-citrullinated protein response and their clinical associations that have been obtained in recent years. These insights include the identification of glycans in the variable domain of ACPA, the realisation that ACPA are polyreactive towards other post-translational modifications on proteins, as well as new awareness of the contributing role of mucosal sites to the development of the ACPA response. These findings will be mirrored to emerging concepts obtained in other human (autoimmune) disease characterised by disease-specific autoantibodies. Together with an updated understanding of genetic and environmental risk factors and fresh perspectives on how the microbiome could contribute to antibody formation, these advancements coalesce to a progressively clearer picture of the B cell reaction to modified antigens in the progression of RA.

Autoantibodies in rheumatoid arthritis - rheumatoid factor, anticitrullinated protein antibodies and beyond

PURPOSE OF REVIEW

RA is characterized by the presence of autoantibodies among which rheumatoid factors (RFs) and antimodified protein antibodies (AMPA) are serological hallmarks of the disease. In recent years, several novel insights into the biology, immunogenetics and clinical relevance of these autoantibodies have been obtained, which deserve to be discussed in more detail.

RECENT FINDINGS

RFs from RA patients seem to target distinct epitopes which appear to be quite specific for RA. Determination of immunoglobulin A (IgA) isotypes of RF and anticitrullinated protein antibodies (ACPA) may provide prognostic information because their presence is associated with reduced therapeutic responses to TNF inhibitors. Furthermore, IgA levels are increased in RA patients and IgA immune complexes are more potent than immunoglobulin G (IgG) complexes in inducing NET formation. Concerning AMPAs, investigations on variable domain glycosylation (VDG) revealed effects on antigen binding and activation of autoreactive B cells. Studies on pathogenetic involvement of ACPA suggest Janus-faced roles: on the one hand, ACPA may be involved in joint destruction and pain perception while on the other hand protective anti-inflammatory effects may be attributed to a subset of ACPAs.

SUMMARY

The autoimmune response in RA is extremely complex and still far from being fully understood. Antibodies are not only valuable diagnostic biomarkers but also seem to play pivotal roles in the pathophysiology of RA.

Neutrophil Extracellular Traps and Respiratory Disease

Extracellular traps made by neutrophils (NETs) and other leukocytes such as macrophages and eosinophils have a key role in the initial immune response to infection but are highly inflammatory and may contribute to tissue damage. They are particularly relevant to lung disease, with the pulmonary anatomy facilitating their ability to fully extend into the airways/alveolar space. There has been a rapid expansion in the number of published studies demonstrating their role in a variety of important respiratory diseases including chronic obstructive pulmonary disease, cystic fibrosis, bronchiectasis, asthma, pneumonia, COVID-19, rhinosinusitis, interstitial lung disease and lung cancer. The expression of NETs and other traps is a specific process, and diagnostic tests need to differentiate them from other inflammatory pathways/causes of cell death that are also characterised by the presence of extracellular DNA. The specific targeting of this pathway by relevant therapeutics may have significant clinical benefit; however, current clinical trials/evidence are at a very early stage. This review will provide a broad overview of the role of NETs and their possible treatment in respiratory disease.

Shift in perspective: autoimmunity protecting against rheumatoid arthritis

A hallmark of rheumatoid arthritis (RA) is the increased levels of autoantibodies preceding the onset and contributing to the classification of the disease. These autoantibodies, mainly anti-citrullinated protein antibody (ACPA) and rheumatoid factor, have been assumed to be pathogenic and many attempts have been made to link them to the development of bone erosion, pain and arthritis. We and others have recently discovered that most cloned ACPA protect against experimental arthritis in the mouse. In addition, we have identified suppressor B cells in healthy individuals, selected in response to collagen type II, and these cells decrease in numbers in RA. These findings provide a new angle on how to explain the development of RA and maybe also other complex autoimmune diseases preceded by an increased autoimmune response.

Neutrophil Extracellular Traps in Tumors and Potential Use of Traditional Herbal Medicine Formulations for Its Regulation

Neutrophil extracellular traps (NETs) are extracellular fibers composed of deoxyribonucleic acid (DNA) and decorated proteins produced by neutrophils. Recently, NETs have been associated with the development of many diseases, including tumors. Herein, we reviewed the correlation between NETs and tumors. In addition, we detailed active compounds from traditional herbal medicine formulations that inhibit NETs, related nanodrug delivery systems, and antibodies that serve as "guiding moieties" to ensure targeted delivery to NETs. Furthermore, we discussed the strategies used by pathogenic microorganisms to evade NETs.

Platelets in Alcohol-Associated Liver Disease: Interaction With Neutrophils

Alcohol-associated liver disease (ALD) is a major contributor to liver-related mortality globally. An increasing body of evidence underscores the pivotal role of platelets throughout the spectrum of liver injury and recovery, offering unique insights into liver homeostasis and pathobiology. Alcoholic-associated steatohepatitis is characterized by the infiltration of hepatic neutrophils. Recent studies have highlighted the extensive distance neutrophils travel through sinusoids to reach the liver injury site, relying on a platelet-paved endothelium for efficient crawling. The adherence of platelets to neutrophils is crucial for accurate migration from circulation to the inflammatory site. A gradual decline in platelet levels leads to diminished neutrophil recruitment. Platelets exhibit the ability to activate neutrophils. Platelet activation is heightened upon the release of platelet granule contents, which synergistically activate neutrophils through their respective receptors. The sequence culminates in the formation of platelet-neutrophil complexes and the release of neutrophil extracellular traps intensifies liver damage, fosters inflammatory immune responses, and triggers hepatotoxic processes. Neutrophil infiltration is a hallmark of alcohol-associated steatohepatitis, and the roles of neutrophils in ALD pathogenesis have been studied extensively, however, the involvement of platelets in ALD has received little attention. The current review consolidates recent findings on the intricate and diverse roles of platelets and neutrophils in liver pathophysiology and in ALD. Potential therapeutic strategies are highlighted, focusing on targeting platelet-neutrophil interactions and activation in ALD. The anticipation is that innovative methods for manipulating platelet and neutrophil functions will open promising avenues for future ALD therapy.

Mercury-containing preparations attenuate neutrophil extracellular trap formation in mice and humans through inhibiting the ERK1/2 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Neutrophil extracellular trap (NET) formation plays a crucial role in wound healing disorders, including chronic skin ulcers and diabetic foot ulcers (DFUs). Over the years, traditional Chinese topical medications, such as Cinnabar (composed of HgS and soluble mercury salt) and hydrargyria oxydum rubrum (containing HgO and soluble mercury salt), have been utilized for treating these ailments. Nevertheless, the fundamental processes remain mostly ambiguous.

AIM OF THE STUDY

This study sought to investigate the potential effects of topical mercury-containing preparations on the process of NET formation.

MATERIALS AND METHODS

Neutrophils isolated from healthy individuals and mouse models of type 1 and type 2 diabetes were cultured with phorbol 12-myristate 13-acetate (PMA), both with and without the mercury-containing preparations (MCP). The formation of NETs was monitored using confocal and scanning electron microscopes. Immunofluorescence and fluorescent probes were employed to assess the levels of citrulline histone H3 (Cit-H3) and intracellular reactive oxygen species (ROS), respectively. The impact of MCP extracts on cytokine expression, peptidylarginine deiminase 4 (PAD4), and myeloperoxidase (MPO) was measured through Luminex and ELISA assays. Phagocytosis of human neutrophils was analyzed using Flow Cytometry. Finally, the phosphorylation levels of ERK were detected by western blotting.

RESULTS

Treatment with MCP led to a reduction in PAD4, Cit-H3, and MPO expressions in neutrophils, consequently inhibiting PMA-induced NET formation. MCP treatment also dampened ERK1/2 activation in neutrophils. Furthermore, MCP exhibited inhibitory effects on the secretion of the cytokine IL-8 and ROS production while enhancing neutrophil phagocytosis.

CONCLUSION

Our findings suggest that MCP can mitigate the release of NETs, likely by suppressing the ERK1/2 signaling pathway.

In early rheumatoid arthritis, anticitrullinated peptide antibodies associate with low number of affected joints and rheumatoid factor associates with systemic inflammation

OBJECTIVES

To investigate how individual rheumatoid arthritis (RA) autoantibodies associate with individual signs and symptoms at the time of RA diagnosis.

METHODS

IgA, IgG, IgM rheumatoid factor (RF), antibodies against cyclic citrullinated peptide version 2 (anti-CCP2) and 16 individual antibodies against citrullinated protein (ACPA) reactivities were analysed centrally in baseline sera from 1600 patients with RA classified according to the 1987 American College of Rheumatology (ACR) criteria. These results were related to C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), number of swollen and tender joints (SJC and TJC), 28-joint disease activity scores (DAS28 and DAS28CRP), global disease activity evaluated by the patients and Health Assessment Questionnaire, all obtained at baseline.

RESULTS

Individually, all autoantibodies except immunoglobulin G (IgG) RF associated with low SJC and TJC and with high ESR. In IgM RF-negative patients, ACPA associated strictly with low number of swollen and tender joints. This association persisted in multiple regression and stratified analyses where IgM and IgA RF instead associated with inflammation expressed as ESR. Among subjects without any ACPA peptide reactivity, there was no association between RF isotypes and ESR. The effect of RF on ESR increased with the number of ACPA reactivities, especially for IgM RF. In patients fulfilling the 1987 ACR criteria without taking RF into account, associations between IgM RF and high ESR, as well as between ACPA and low joint counts, remained.

CONCLUSION

Whereas ACPA associate with low counts of affected joints in early RA, RF associates with elevated measures of systemic inflammation in an ACPA-dependent manner. This latter finding corroborates in vitro models of ACPA and RF in immune complex-induced inflammation. These phenotypic associations are independent of classification criteria.

B Cells Dynamic in Aging and the Implications of Nutritional Regulation

Aging negatively affects B cell production, resulting in a decrease in B-1 and B-2 cells and impaired antibody responses. Age-related B cell subsets contribute to inflammation. Investigating age-related alterations in the B-cell pool and developing targeted therapies are crucial for combating autoimmune diseases in the elderly. Additionally, optimal nutrition, including carbohydrates, amino acids, vitamins, and especially lipids, play a vital role in supporting immune function and mitigating the age-related decline in B cell activity. Research on the influence of lipids on B cells shows promise for improving autoimmune diseases. Understanding the aging B-cell pool and considering nutritional interventions can inform strategies for promoting healthy aging and reducing the age-related disease burden.

Anti-Citrullinated Protein Antibodies With Multiple Specificities Ameliorate Collagen Antibody-Induced Arthritis in a Time-Dependent Manner

OBJECTIVE

Anti-citrullinated protein antibodies (ACPAs) are highly specific for rheumatoid arthritis (RA) and have long been regarded as pathogenic. Despite substantial in vitro evidence supporting this claim, reports investigating the proinflammatory effects of ACPAs in animal models of arthritis are rare and include mixed results. Here, we sequenced the plasmablast antibody repertoire of a patient with RA and functionally characterized the encoded ACPAs.

METHODS

We expressed ACPAs from the antibody repertoire of a patient with RA and characterized their autoantigen specificities on antigen arrays and enzyme-linked immunosorbent assays. Binding affinities were estimated by bio-layer interferometry. Select ACPAs (n = 9) were tested in the collagen antibody-induced arthritis (CAIA) mouse model to evaluate their effects on joint inflammation.

RESULTS

Recombinant ACPAs bound preferentially and with high affinity (nanomolar range) to citrullinated (cit) autoantigens (primarily histones and fibrinogen) and to auto-cit peptidylarginine deiminase 4 (PAD4). ACPAs were grouped for in vivo testing based on their predominant cit-antigen specificities. Unexpectedly, injections of recombinant ACPAs significantly reduced paw thickness and arthritis severity in CAIA mice as compared with isotype-matched control antibodies (P ≤ 0.001). Bone erosion, synovitis, and cartilage damage were also significantly reduced (P ≤ 0.01). This amelioration of CAIA was observed for all the ACPAs tested and was independent of cit-PAD4 and cit-fibrinogen specificities. Furthermore, disease amelioration was more prominent when ACPAs were injected at earlier stages of CAIA than at later phases of the model.

CONCLUSION

Recombinant patient-derived ACPAs ameliorated CAIA. Their antiinflammatory effects were more preventive than therapeutic. This study highlights a potential protective role for ACPAs in arthritis.

Symptoms and Management of Aseptic Liver Abscesses

Aseptic liver abscesses occur very rarely. Clinical guidelines on the management of the disease do not exist, and the diagnosis is challenging.We screen MEDLINE and PUBMED databases for relevant case reports from inception to November 2022. Information on patient age, sex, initial symptoms, the extent of abscess formation, further diagnoses, treatment, and course of the disease is analyzed.Thirty cases with sterile hepatic abscess formation are identified. In most patients (n=18), the spleen is affected as well. Patients typically present with fever, abdominal pain, and increased inflammatory values. Comorbidity with inflammatory bowel disease is very common (n=18) and is associated with a significantly younger age at the time of hepatic abscess development. In addition, many patients show autoimmune-mediated cutaneous, ocular, or arthritic rheumatoid manifestations. Histological examination of abscess material reveals neutrophilic infiltration. The majority of patients initially receive corticosteroid therapy. Furthermore, response to azathioprine, anti-TNF-α antibodies, and other immunomodulatory drugs is reported. Ten out of fourteen patients with a long-term follow-up (≥ 36 months) have at least one relapse of hepatic abscess formation.Aseptic hepatic abscesses should be considered in the case of sterile punctures and non-response to antibiotics. Patients with aseptic liver abscesses have a high risk of recurrence warranting immunomodulatory maintenance therapy.

Neutrophil extracellular traps in adult diseases and neonatal bacterial infectious diseases: A review

Neutrophils, the most abundant type of white blood cells, are pivotal in fighting bacterial infections due to their immunological and anti-infection capabilities. In recent years, scientists have discovered a novel mechanism known as neutrophil extracellular traps, which are fibrous networks primarily released by neutrophils that combat bacterial infections. There is a growing interest in studying NETs and their role in human infectious diseases, particularly in neonates susceptible to bacterial infections. NETs and their components have been found in various samples from neonatal-infected patients, providing a new route for early diagnosis of neonatal infectious diseases. This paper aims to summarize the studies on NETs in adult diseases and mainly discuss NETs in neonatal sepsis, necrotizing enterocolitis, and purulent meningitis, to provide scientific evidence for early monitoring, diagnosis, and treatment of neonatal infections.

Can Serum Histone H4 Level Be a Biomarker in Ulcerative Colitis?

BACKGROUND/AIMS

Histones are a part of neutrophil extracellular trap molecules which were reported to have diagnostic values in some inflammatory diseases. We aimed to evaluate whether serum histone H4 can be a diagnostic and prognostic marker for ulcerative colitis.

MATERIALS AND METHODS

This case-control study included 58 ulcerative colitis patients (34 males and 24 females) and 45 healthy controls (25 males and 20 females). The Mayo clinical scoring system was used for the clinical and endoscopic features. Truelove-Witt's method was applied to the histology activity index. The human histone H4 kit was used for the enzyme-linked immunosorbent assay of serum histone H4.

RESULTS

Serum histone H4 was significantly lower in the ulcerative colitis group compared to the control groups [268 (14-1639) vs. 598 (310-2134) ng/L, P < .001, respectively]. Among the ulcerative colitis patients, there was no correlation between serum histone H4 and disease extent, Mayo clinical scoring, Mayo endoscopic activity subscoring, histology activity index, inflammatory markers, d-dimer, and leukocyte and neutrophil counts (r < 0.20, P > .05). Histone H4 levels were not statistically significant between the patients with no medication and those taking 5-aminosalicylate and/or other agents (P > .05). The receiver operating characteristic curve analysis revealed that serum histone H4 concentrations had a 0.782 (95%CI: 0.690-0.857, P < .001) diagnostic accuracy for ulcerative colitis. The specificity and sensitivity for the cutoff level of ≤364 ng/L were 88.9% and 72.4%, respectively.

CONCLUSION

Decreased serum histone H4 values may be used as an auxiliary marker in the progression and diagnosis of ulcerative colitis. Further studies are needed to delineate this relationship between clinical and laboratory traits of ulcerative colitis and serum histone H4.

Neutrophil extracellular traps regulating tumorimmunity in hepatocellular carcinoma

As a component of the innate immune system, there is emerging evidence to suggest that neutrophils may play a critical role in the initiation and progression of hepatocellular carcinoma (HCC). Neutrophil extracellular traps (NETs) are web-like chromatin structures that protrude from the membranes during neutrophil activation. Recent research has shown that NETs, which are at the forefront of the renewed interest in neutrophil studies, are increasingly intertwined with HCC. By exploring the mechanisms of NETs in HCC, we aim to improve our understanding of the role of NETs and gain deeper insights into neutrophil biology. Therefore, this article provides a summary of key findings and discusses the emerging field of NETs in HCC.

Neutrophils in Inflammatory Diseases: Unraveling the Impact of Their Derived Molecules and Heterogeneity

Inflammatory diseases involve numerous disorders and medical conditions defined by an insufficient level of self-tolerance. These diseases evolve over the course of a multi-step process through which environmental variables play a crucial role in the emergence of aberrant innate and adaptive immunological responses. According to experimental data accumulated over the past decade, neutrophils play a significant role as effector cells in innate immunity. However, neutrophils are also involved in the progression of numerous diseases through participation in the onset and maintenance of immune-mediated dysregulation by releasing neutrophil-derived molecules and forming neutrophil extracellular traps, ultimately causing destruction of tissues. Additionally, neutrophils have a wide variety of functional heterogeneity with adverse effects on inflammatory diseases. However, the complicated role of neutrophil biology and its heterogeneity in inflammatory diseases remains unclear. Moreover, neutrophils are considered an intriguing target of interventional therapies due to their multifaceted role in a number of diseases. Several approaches have been developed to therapeutically target neutrophils, involving strategies to improve neutrophil function, with various compounds and inhibitors currently undergoing clinical trials, although challenges and contradictions in the field persist. This review outlines the current literature on roles of neutrophils, neutrophil-derived molecules, and neutrophil heterogeneity in the pathogenesis of autoimmune and inflammatory diseases with potential future therapeutic strategies.

Thymopentin ameliorates experimental colitis via inhibiting neutrophil extracellular traps

BACKGROUND

The long-term prognosis of Crohn's disease (CD) remains unsatisfactory. Therefore, we assessed the therapeutic effect of thymopentin (TP5) in a mouse model of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis, which mimics CD, and analyzed its impact on neutrophil extracellular traps (NETs).

METHODS

NET markers, including myeloperoxidase (MPO), neutrophil elastase (NE), citrullinated histone H3 (CitH3), peptidyl arginine deiminase IV (PAD4), and double-stranded DNA (dsDNA) were assessed by immunostaining and enzyme-linked immunosorbent assay. NET formation was evaluated in vitro. Neoseptin 3, a specific NET agonist, was used to reverse the effect of TP5 on TNBS-induced colitis. The action mechanism of TP5 was investigated using RNA-seq.

RESULTS

TP5 ameliorated weight loss (P < 0.001), disease activity index (DAI) (P = 0.05), colon shrinkage (P = 0.04), and elevated levels of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β, IL-6, and neutrophils in the TNBS group. The TNBS group exhibited increased MPO, NE, CitH3, PAD4, dsDNA and MPO-DNA levels (all P < 0.001), which decreased after TP5 administration (P = 0.01, P < 0.001, P < 0.001, P < 0.001, P = 0.02, and P = 0.02 respectively). Tissue CitH3 levels were positively correlated with DAI and TNF-α levels (P < 0.05). Furthermore, phorbol 12-myristate 13-acetate-stimulated NET formation increased by 1.8-, 2.8-, and 2.3-fold in vitro in the control, TNBS + saline, and TNBS + TP5 groups, respectively. Neoseptin 3 significantly reversed the effect of TP5. RNA-seq revealed potential pathways underlying the effect of TP5.

CONCLUSION

TP5 effectively ameliorated colitis by suppressing NETs in the experimental CD model.

Rethinking neutrophil extracellular traps

Neutrophils are a major subset of leukocytes in human circulating blood. In some circumstances, neutrophils release neutrophil extracellular traps (NETs). lnitially, NETs were considered to have a strong antibacterial capacity. However, currently, NETs have been shown to have a pivotal impact on various diseases. Different stimulators induce the production of different types of NETs, and their biological functions and modes of clearance do not appear to be the same. In this review, we will discuss several important issues related to NETs in order to better understand the relationship between NETs and diseases, as well as how to utilize the characteristics of NETs for disease treatment.

Blockade of IL-18Rα-mediated signaling pathway exacerbates neutrophil infiltration in imiquimod-induced psoriasis murine model

Psoriasis is an immune-mediated inflammatory disease of the skin, which is characterized by epidermal hyperkeratosis and neutrophil infiltration. The interleukin (IL)-17/IL-23 pathway and associated cytokines play major roles in the pathogenesis and exacerbation of psoriasis. The IL-18/IL-18 receptor (R) α signaling pathway is important for Th1 cytokine production and differentiation of Th1 cells; however, its role in the pathogenesis of psoriasis remains unknown. In this study, we investigated the effect of the IL-18Rα-mediated signaling pathway in the pathogenesis of psoriasis in Il18ra-deficient mice (Il18ra-/-) and wild-type imiquimod (IMQ)-induced psoriatic dermatitis model mice. Blocking this pathway exacerbated IMQ-induced psoriatic skin inflammation. Il18ra deficiency led to significant increases in the levels of IL-1β, IL-6, IL-8, IL-17A, IL-23, and chemokine (C-X-C motif) ligand 2 in skin lesions. Gr1-positive cells highly infiltrated psoriatic skin lesions in Il18ra-/- mice compared to those in wild-type mice. Citrullinated histone H3-positive area was relatively broad in Il18ra-/- mice. These results suggest that IL-18Rα-mediated signaling pathways may inhibit psoriatic skin inflammation by regulating infiltration and activation of neutrophil and other innate immune cells.

Advances in proteomics: characterization of the innate immune system after birth and during inflammation

Proteomics is the characterization of the protein composition, the proteome, of a biological sample. It involves the large-scale identification and quantification of proteins, peptides, and post-translational modifications. This review focuses on recent developments in mass spectrometry-based proteomics and provides an overview of available methods for sample preparation to study the innate immune system. Recent advancements in the proteomics workflows, including sample preparation, have significantly improved the sensitivity and proteome coverage of biological samples including the technically difficult blood plasma. Proteomics is often applied in immunology and has been used to characterize the levels of innate immune system components after perturbations such as birth or during chronic inflammatory diseases like rheumatoid arthritis (RA) and inflammatory bowel disease (IBD). In cancers, the tumor microenvironment may generate chronic inflammation and release cytokines to the circulation. In these situations, the innate immune system undergoes profound and long-lasting changes, the large-scale characterization of which may increase our biological understanding and help identify components with translational potential for guiding diagnosis and treatment decisions. With the ongoing technical development, proteomics will likely continue to provide increasing insights into complex biological processes and their implications for health and disease. Integrating proteomics with other omics data and utilizing multi-omics approaches have been demonstrated to give additional valuable insights into biological systems.

Role and Therapeutic Targeting Strategies of Neutrophil Extracellular Traps in Inflammation

Neutrophil extracellular traps (NETs) are large DNA reticular structures secreted by neutrophils and decorated with histones and antimicrobial proteins. As a key mechanism for neutrophils to resist microbial invasion, NETs play an important role in the killing of microorganisms (bacteria, fungi, and viruses). Although NETs are mostly known for mediating microbial killing, increasing evidence suggests that excessive NETs induced by stimulation of physical and chemical components, microorganisms, and pathological factors can exacerbate inflammation and organ damage. This review summarizes the induction and role of NETs in inflammation and focuses on the strategies of inhibiting NETosis and the mechanisms involved in pathogen evasion of NETs. Furthermore, herbal medicine inhibitors and nanodelivery strategies improve the efficiency of inhibition of excessive levels of NETs.

Neutrophil extracellular traps contributing to atherosclerosis: From pathophysiology to clinical implications

Neutrophil extracellular traps (NETs) are network-like structures of chromatin filaments decorated by histones, granules, and cytoplasmic-derived proteins expelled by activated neutrophils under multiple pathogenic conditions. NETs not only capture pathogens in innate immunity but also respond to sterile inflammatory stimuli in atherosclerosis, such as lipoproteins and inflammatory cytokines. Atherosclerosis is a lipid-driven chronic inflammatory disease characterized by the accumulation and transformation of inflammatory cells, and smooth muscle cells in the intimal space. NETs-derived extracellular components possess toxic and proinflammatory properties leading to cellular dysfunction and tissue damage, which may establish a link among lipid metabolism, inflammatory immunity, and atherosclerosis. In this review, we discuss recent advances regarding the role of NETs engaged in the pathogenesis of atherosclerosis, particularly focusing on the interaction with lipids and inflammasomes, crosstalk with smooth muscle cells and inflammatory cells, and the association with aging. We also evaluate the current knowledge on the potential of NETs as biomarkers and therapeutic targets for atherosclerosis and its related diseases in clinical practice.

Anti-citrullinated protein antibodies as biomarkers in rheumatoid arthritis

INTRODUCTION

The serological biomarker anti-citrullinated protein antibodies (ACPAs) may have several functions but is especially important for the diagnosis of rheumatoid arthritis (RA) along with clinical symptoms.

AREAS COVERED

This review provides an overview of ACPAs, which are useful in RA diagnostics and may improve our understanding of disease etiology. PubMed was searched with combinations of words related to antibodies recognizing epitopes containing the post-translationally modified amino acid citrulline in combination with rheumatoid arthritis; cyclic citrullinated peptide, CCP, anti-CCP, anti-citrullinated protein antibodies, ACPA, citrullination, peptide/protein arginine deiminase, PAD, filaggrin, vimentin, keratin, collagen, perinuclear factor, EBNA1, EBNA2, and others. From this search, we made a qualitative extract of publications relevant to the discovery, characterization, and clinical use of these antibodies in relation to RA. We highlight significant findings and identify areas for improvement.

EXPERT OPINION

ACPAs have high diagnostic sensitivity and specificity for RA and recognize citrullinated epitopes from several proteins. The best-performing single epitope originates from Epstein-Barr Virus nuclear antigen 2 and contains a central Cit-Gly motif, which is recognized by ACPAS when located in a flexible peptide structure. In addition, ACPAs may also have prognostic value, especially in relation to early treatment, although ACPAs' main function is to aid in the diagnosis of RA.

The effect of neutrophil extracellular traps in venous thrombosis

Neutrophil extracellular traps (NETs) as special release products of neutrophils have received extensive attention. They are composed of decondensed chromatin and coated with nucleoproteins, including histones and some granulosa proteins. NETs can form a network structure to effectively capture and eliminate pathogens and prevent their spread. Not only that, recent studies have shown that NETs also play an important role in venous thrombosis. This review provides the most important updated evidence regarding the mechanism of NETs formation and the role of NETs in the process of venous thrombosis. The potential prophylactic and therapeutic value of NETs in venous thrombotic disease will also be discussed.

Bladder cancer patients have increased NETosis and impaired DNaseI-mediated NET degradation that can be therapeutically restored in vitro

Background

Neutrophils, key players of the immune system, also promote tumor development through the formation of neutrophil extracellular traps (NETs) in a process called NETosis. NETs are extracellular networks of DNA, histones and cytoplasmic and granular proteins (calprotectin, myeloperoxidase, elastase, etc.) released by neutrophils upon activation. NETs regulate tumor growth while promoting angiogenesis and invasiveness, and tumor cells also stimulate NETosis. Although NETosis seems to be increased in cancer patients, an increase of NETs in plasma may also be mediated by an impaired degradation by plasma DNaseI, as evidenced in several immunological disorders like lupus nephritis. However, this has never been evidenced in bladder cancer (BC) patients. Herein, we aimed to evaluate the occurrence of increased NETosis in plasma and tumor tissue of BC patients, to ascertain whether it is mediated by a reduced DNaseI activity and degradation, and to in vitro explore novel therapeutic interventions.

Methods

We recruited 71 BC patients from whom we obtained a plasma sample before surgery and a formalin-fixed paraffin embedded tumor tissue sample, and 64 age- and sex-matched healthy controls from whom we obtained a plasma sample. We measured NETs markers (cell-free fDNA, calprotectin, nucleosomes and neutrophil elastase) and the DNaseI activity in plasma with specific assays. We also measured NETs markers in BC tissue by immunofluorescence. Finally, we evaluated the ability of BC and control plasma to degrade in vitro-generated NETs, and evaluated the performance of the approved recombinant human DNaseI (rhDNaseI, Dornase alfa, Pulmozyme^®, Roche) to restore the NET-degradation ability of plasma. In vitro experiments were performed in triplicate. Statistical analysis was conducted with Graphpad (v.8.0.1).

Results

NETosis occurs in BC tissue, more profusely in the muscle-invasive subtype (P<0.01), that with the worst prognosis. Compared to controls, BC patients had increased NETosis and a reduced DNaseI activity in plasma (P<0.0001), which leads to an impairment to degrade NETs (P<0.0001). Remarkably, this can be therapeutically restored with rhDNaseI to the level of healthy controls.

Conclusion

To the best of our knowledge, this is the first report demonstrating that BC patients have an increased NETosis systemically and in the tumor microenvironment, in part caused by an impaired DNaseI-mediated NET degradation. Remarkably, this defect can be therapeutically restored in vitro with the approved Dornase alfa, thus Pulmozyme^® could become a potential therapeutic tool to locally reduce BC progression.