Evidence of eosinophil extracellular trap cell death in COPD: does it represent the trigger that switches on the disease?

The challenge of diagnosing and classifying eosinophilia and eosinophil disorders: A review

Eosinophilia is a feature of multiple conditions, both hematologic and non-hematologic, and may be associated with organ damage. The pathogenesis of eosinophilia can follow two distinct pathways. Primary eosinophilia is caused by a cell-intrinsic mechanism originating from clonal expansion of eosinophils through acquisition of a somatic mutation, such as FIP1L1-PDGFRA. In recent years, great progress has been made in the field of pathogenesis and molecularly targeted therapy of neoplastic eosinophilia. The diagnostic procedure should include, among other things, morphologic analysis of blood and bone marrow samples, cytogenetics and fluorescence in situ-hybridization tests to detect evidence of an acute or chronic myeloid or lymphoid disorder. Secondary eosinophilia follows a cell-extrinsic mechanism as a response to exogenous cytokines. In most clinical cases, peripheral blood eosinophilia is reactive and typically associated with non-hematological disorders such as infections, allergic conditions, connective tissue disorders, vasculitis, malignancy, or endocrinopathies. Nonetheless, the cause of most cases of hypereosinophilic syndrome remains unknown. In this article, we present a short review focused on differential diagnosis of eosinophilia and eosinophilic disorders. The diagnosis of eosinophilia is a challenge for physicians; thus this review may be useful in clinical practice.

Extracellular traps are evident in Romanowsky-stained smears of bronchoalveolar lavage from children with non-cystic fibrosis bronchiectasis

BACKGROUND AND OBJECTIVE

The importance of extracellular traps (ETs) in chronic respiratory conditions is increasingly recognized but their role in paediatric bronchiectasis is poorly understood. The specialized techniques currently required to study ETs preclude routine clinical use. A simple and cost-effective ETs detection method is needed to support diagnostic applications. We aimed to determine whether ETs could be detected using light microscopy-based assessment of Romanowsky-stained bronchoalveolar lavage (BAL) slides from children with bronchiectasis, and whether the ETs cellular origin could be determined.

METHODS

Archived Romanowsky-stained BAL slides from a cross-sectional study of children with bronchiectasis were examined for ETs using light microscopy. The cellular origin of individual ETs was determined based on morphology and physical contact with surrounding cell(s).

RESULTS

ETs were observed in 78.7% (70/89) of BAL slides with neutrophil (NETs), macrophage (METs), eosinophil (EETs) and lymphocyte (LETs) ETs observed in 32.6%, 51.7%, 4.5% and 9%, respectively. ETs of indeterminate cellular origin were present in 59.6% of slides. Identifiable and indeterminate ETs were co-detected in 43.8% of slides.

CONCLUSION

BAL from children with bronchiectasis commonly contains multiple ET types that are detectable using Romanowsky-stained slides. While specialist techniques remain necessary to determining the cellular origin of all ETs, screening of Romanowsky-stained slides presents a cost-effective method that is well-suited to diagnostic settings. Our findings support further research to determine whether ETs can be used to define respiratory endotypes and to understand whether ETs-specific therapies may be required to resolve airway inflammation among children with bronchiectasis.

An Emerging Role of Extracellular Traps in Chronic Rhinosinusitis

PURPOSE OF REVIEW

Chronic rhinosinusitis (CRS) is a complicated, heterogeneous disease likely caused by inflammatory and infectious factors. There is clear evidence that innate immune cells, including neutrophils and eosinophils, play a significant role in CRS. Multiple immune cells, including neutrophils and eosinophils, have been shown to release chromatin and granular proteins into the extracellular space in response to triggering extracellular traps (ETs). The formation of ETs remains controversial due to their critical function during pathogen clearance while being associated with harmful inflammatory illnesses. This article summarizes recent research on neutrophil extracellular traps (NETs) and eosinophil extracellular traps (EETs) and their possible significance in the pathophysiology of CRS.

RECENT FINDINGS

A novel type of programmed cell death called ETosis, which releases ETs, has been proposed by recent study. Significantly more NETs are presented in nasal polyps, and its granule proteins LL-37 induce NETs production in CRS with nasal polyps (CRSwNP) patients. Similar to NETs, developed in the tissue of nasal polyps, primarily in subepithelial regions with epithelial barrier defects, and are associated with linked to elevated tissue levels of IL-5 and S. aureus colonization. This article provides a comprehensive overview of NETs and EETs, as well as an in-depth understanding of the functions of these ETs in CRS.

Current insights into the role of citrullination in thrombosis

Protein citrullination is a post-translational modification of arginine that controls a diverse array of cellular processes, including gene regulation, protein stability, and neutrophil extracellular trap (NET) formation. Histone citrullination promotes chromatin decondensation and NET formation, a pro-inflammatory form of cell death that is aberrantly increased in numerous immune disorders. This review will provide insights into NETosis and how this novel form of cell death contributes to inflammatory diseases, with a particular emphasis on its role in thrombosis. We will also discuss recent efforts to develop PAD-specific inhibitors.

Different modalities of host cell death and their impact on Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (Mtb) is the pathogen that causes tuberculosis (TB), a leading infectious disease of humans worldwide. One of the main histopathological hallmarks of TB is the formation of granulomas comprised of elaborately organized aggregates of immune cells containing the pathogen. Dissemination of Mtb from infected cells in the granulomas due to host and mycobacterial factors induces multiple cell death modalities in infected cells. Based on molecular mechanism, morphological characteristics, and signal dependency, there are two main categories of cell death: programmed and nonprogrammed. Programmed cell death (PCD), such as apoptosis and autophagy, is associated with a protective response to Mtb by keeping the bacteria encased within dead macrophages that can be readily phagocytosed by arriving in uninfected or neighboring cells. In contrast, non-PCD necrotic cell death favors the pathogen, resulting in bacterial release into the extracellular environment. Multiple types of cell death in the PCD category, including pyroptosis, necroptosis, ferroptosis, ETosis, parthanatos, and PANoptosis, may be involved in Mtb infection. Since PCD pathways are essential for host immunity to Mtb, therapeutic compounds targeting cell death signaling pathways have been experimentally tested for TB treatment. This review summarizes different modalities of Mtb-mediated host cell deaths, the molecular mechanisms underpinning host cell death during Mtb infection, and its potential implications for host immunity. In addition, targeting host cell death pathways as potential therapeutic and preventive approaches against Mtb infection is also discussed.

Galectin-10 as a Potential Biomarker for Eosinophilic Diseases

Galectin-10 is a member of the lectin family and one of the most abundant cytoplasmic proteins in human eosinophils. Except for some myeloid leukemia cells, basophils, and minor T cell populations, galectin-10 is exclusively present in eosinophils in the human body. Galectin-10 forms Charcot–Leyden crystals, which are observed in various eosinophilic diseases. Accumulating studies have indicated that galectin-10 acts as a new biomarker for disease activity, diagnosis, and treatment effectiveness in asthma, eosinophilic esophagitis, rhinitis, sinusitis, atopic dermatitis, and eosinophilic granulomatosis with polyangiitis. The extracellular release of galectin-10 is not mediated through conventional secretory processes (piecemeal degranulation or exocytosis), but rather by extracellular trap cell death (ETosis), which is an active cell death program. Eosinophils undergoing ETosis rapidly disintegrate their plasma membranes to release the majority of galectin-10. Therefore, elevated galectin-10 levels in serum and tissue suggest a high degree of eosinophil ETosis. To date, several studies have shown that galectin-10/Charcot–Leyden crystals are more than just markers for eosinophilic inflammation, but play functional roles in immunity. In this review, we focus on the close relationship between eosinophils and galectin-10, highlighting this protein as a potential new biomarker in eosinophilic diseases.

Extracellular traps and the role in thrombosis

Thrombotic complications pose serious health risks worldwide. A significant change in our understanding of the pathophysiology of thrombosis has occurred since the discovery of extracellular traps (ETs) and their prothrombotic properties. As a result of immune cells decondensing chromatin into extracellular fibers, ETs promote thrombus formation by acting as a scaffold that activates platelets and coagulates them. The involvement of ETs in thrombosis has been reported in various thrombotic conditions including deep vein thrombosis (DVT), pulmonary emboli, acute myocardial infarction, aucte ischemic stroke, and abdominal aortic aneurysms. This review summarizes the existing evidence of ETs in human and animal model thrombi. The authors described studies showing the existence of ETs in venous or arterial thrombi. In addition, we studied potential novel therapeutic opportunities related to the resolution or prevention of thrombosis by targeting ETs.

In Vivo ETosis of Human Eosinophils: The Ultrastructural Signature Captured by TEM in Eosinophilic Diseases

Eosinophilic diseases, also termed eosinophil-associated diseases (EADs), are characterized by eosinophil-rich inflammatory infiltrates and extensive eosinophil degranulation with clinically relevant organ pathology. Recent evidence shows that eosinophil cytolytic degranulation, that is, the release of intact, membrane-delimited granules that arises from the eosinophil cytolysis, occurs mainly through ETosis, meaning death with a cytolytic profile and extrusion of nucleus-originated DNA extracellular traps (ETs). The ultrastructural features of eosinophil ETosis (EETosis) have been studied mostly in vitro after stimulation, but are still poorly understood in vivo. Here, we investigated in detail, by transmission electron microscopy (TEM), the ultrastructure of EETosis in selected human EADs affecting several tissues and organ systems. Biopsies of patients diagnosed with eosinophilic chronic rhinosinusitis/ECRS (frontal sinus), ulcerative colitis/UC (intestine), and hypereosinophilic syndrome/HES (skin) were processed for conventional TEM. First, we found that a large proportion of tissue-infiltrated eosinophils in all diseases (~45-65% of all eosinophils) were undergoing cytolysis with release of free extracellular granules (FEGs). Second, we compared the morphology of tissue inflammatory eosinophils with that shown by in vitro ETosis-stimulated eosinophils. By applying single-cell imaging analysis, we sought typical early and late EETosis events: chromatin decondensation; nuclear delobulation and rounding; expanded nuclear area; nuclear envelope alterations and disruption; and extracellular decondensed chromatin spread as ETs. We detected that 53% (ECRS), 37% (UC), and 82% (HES) of all tissue cytolytic eosinophils had ultrastructural features of ETosis in different degrees. Eosinophils in early ETosis significantly increased their nuclear area compared to non-cytolytic eosinophils due to excessive chromatin decondensation and expansion observed before nuclear envelope disruption. ETosis led not only to the deposition of intact granules, but also to the release of eosinophil sombrero vesicles (EoSVs) and Charcot-Leyden crystals (CLCs). Free intact EoSVs and CLCs were associated with FEGs and extracellular DNA nets. Interestingly, not all cytolytic eosinophils in the same microenvironment exhibited ultrastructure of ETosis, thus indicating that different populations of eosinophils might be selectively activated into this pathway. Altogether, our findings captured an ultrastructural signature of EETosis in vivo in prototypic EADs highlighting the importance of this event as a form of eosinophil degranulation and release of inflammatory markers (EoSVs and CLCs).

Unveiling Leukocyte Extracellular Traps in Inflammatory Responses of the Central Nervous System

Over the past nearly two decades, increasing evidence has uncovered how immune cells can actively extrude genetic material to entrap invading pathogens or convey sterile inflammatory signals that contribute to shaping immune responses. Originally identified in neutrophils, the release of decondensed chromatin fibers decorated with antimicrobial proteins, called extracellular traps (ETs), has been recognized as a specific form of programmed inflammatory cell death, which is now known to occur in several other leukocytes. Subsequent reports have shown that self-DNA can be extruded from immune cells even in the absence of cell death phenomena. More recent data suggest that ETs formation could exacerbate neuroinflammation in several disorders of the central nervous system (CNS). This review article provides an overview of the varied types, sources, and potential functions of extracellular DNA released by immune cells. Key evidence suggesting the involvement of ETs in neurodegenerative, traumatic, autoimmune, and oncological disorders of the CNS will be discussed, outlining ongoing challenges and drawing potentially novel lines of investigation.

Extracellular DNA Traps: Origin, Function and Implications for Anti-Cancer Therapies

Extracellular DNA may serve as marker in liquid biopsies to determine individual diagnosis and prognosis in cancer patients. Cell death or active release from various cell types, including immune cells can result in the release of DNA into the extracellular milieu. Neutrophils are important components of the innate immune system, controlling pathogens through phagocytosis and/or the release of neutrophil extracellular traps (NETs). NETs also promote tumor progression and metastasis, by modulating angiogenesis, anti-tumor immunity, blood clotting and inflammation and providing a supportive niche for metastasizing cancer cells. Besides neutrophils, other immune cells such as eosinophils, dendritic cells, monocytes/macrophages, mast cells, basophils and lymphocytes can also form extracellular traps (ETs) during cancer progression, indicating possible multiple origins of extracellular DNA in cancer. In this review, we summarize the pathomechanisms of ET formation generated by different cell types, and analyze these processes in the context of cancer. We also critically discuss potential ET-inhibiting agents, which may open new therapeutic strategies for cancer prevention and treatment.

Inflammation: A New Look at an Old Problem

Pro-inflammatory stress is inherent in any cells that are subject to damage or threat of damage. It is defined by a number of universal components, including oxidative stress, cellular response to DNA damage, unfolded protein response to mitochondrial and endoplasmic reticulum stress, changes in autophagy, inflammasome formation, non-coding RNA response, formation of an inducible network of signaling pathways, and epigenetic changes. The presence of an inducible receptor and secretory phenotype in many cells is the cause of tissue pro-inflammatory stress. The key phenomenon determining the occurrence of a classical inflammatory focus is the microvascular inflammatory response (exudation, leukocyte migration to the alteration zone). This same reaction at the systemic level leads to the development of life-critical systemic inflammation. From this standpoint, we can characterize the common mechanisms of pathologies that differ in their clinical appearance. The division of inflammation into alternative variants has deep evolutionary roots. Evolutionary aspects of inflammation are also described in the review. The aim of the review is to provide theoretical arguments for the need for an up-to-date theory of the relationship between key human pathological processes based on the integrative role of the molecular mechanisms of cellular and tissue pro-inflammatory stress.

A sputum 6-gene signature predicts airway inflammation endotypes and exacerbation frequency in chronic obstructive pulmonary disease

Aim: To validate a sputum 6-gene signature (6GS), comprising of CLC, CPA, DNASE1L3, IL-1B, ALPL and CXCR2, for identifying different endotypes in chronic obstructive pulmonary disease. Methodology & results: Sputum cell CLC, CPA3 and DNASE1L3 gene expression correlated with eosinophil percentage, while IL-1B, ALPL and CXCR2 correlated with neutrophil percentage. Hierarchical cluster analyses of IL-1B, ALPL and CXCR2, and CLC, CPA3 and DNASE1L3, identified patient groups that differed in their sputum neutrophil and eosinophil levels, respectively. Multiple logistic regressions demonstrated that the 6GS could distinguish between eosinophil^High and eosinophil^Low patients, as well as neutrophil^High and neutrophil^Low, and could also predict exacerbation history. Conclusion: The 6GS may have applications in clinical practice or for stratifying patients for clinical trials.

Role of Extracellular Trap Release During Bacterial and Viral Infection

Neutrophils are innate immune cells that play an essential role during the clearance of pathogens that can release chromatin structures coated by several cytoplasmatic and granular antibacterial proteins, called neutrophil extracellular traps (NETs). These supra-molecular structures are produced to kill or immobilize several types of microorganisms, including bacteria and viruses. The contribution of the NET release process (or NETosis) to acute inflammation or the prevention of pathogen spreading depends on the specific microorganism involved in triggering this response. Furthermore, studies highlight the role of innate cells different from neutrophils in triggering the release of extracellular traps during bacterial infection. This review summarizes the contribution of NETs during bacterial and viral infections, explaining the molecular mechanisms involved in their formation and the relationship with different components of such pathogens.

Neutrophil and Eosinophil DNA Extracellular Trap Formation: Lessons From Pathogenic Fungi

Fungal infections represent a worldwide health problem. Fungal pathogens are responsible for a variety of conditions, including superficial diseases, allergic pathologies and potentially lethal invasive infections. Neutrophils and eosinophils have been implicated as effector cells in several pathologies. Neutrophils are major effector cells involved in the control of fungal infections and exhibit a plethora of antifungal mechanisms, such as phagocytosis, reactive oxygen species production, degranulation, extracellular vesicle formation, and DNA extracellular trap (ET) release. Eosinophils are polymorphonuclear cells classically implicated as effector cells in the pathogenesis of allergic diseases and helminthic infections, although their roles as immunomodulatory players in both innate and adaptive immunity are currently recognized. Eosinophils are also endowed with antifungal activities and are abundantly found in allergic conditions associated with fungal colonization and sensitization. Neutrophils and eosinophils have been demonstrated to release their nuclear and mitochondrial DNA in response to many pathogens and pro-inflammatory stimuli. ETs have been implicated in the killing and control of many pathogens, as well as in promoting inflammation and tissue damage. The formation of ETs by neutrophils and eosinophils has been described in response to pathogenic fungi. Here, we provide an overview of the mechanisms involved in the release of neutrophil and eosinophil ETs in response to fungal pathogens. General implications for understanding the formation of ETs and the roles of ETs in fungal infections are discussed.

How to detect eosinophil ETosis (EETosis) and extracellular traps

Eosinophils are short-lived and comprise only a small population of circulating leukocytes; however, they play surprisingly multifunctional roles in homeostasis and various diseases including allergy and infection. Recent research has shed light on active cytolytic eosinophil cell death that releases eosinophil extracellular traps (EETs) and total cellular contents, namely eosinophil extracellular trap cell death (EETosis). The pathological contribution of EETosis was made more cogent by recent findings that a classical pathological finding of eosinophilic inflammation, that of Charcot-Leyden crystals, is closely associated with EETosis. Currently no gold standard methods to identify EETosis exist, but “an active eosinophil lysis that releases cell-free granules and net-like chromatin structure” appears to be a common feature of EETosis. In this review, we describe several approaches that visualize EETs/EETosis in clinical samples and in vitro studies using isolated human eosinophils. EETs/EETosis can be observed using simple chemical or fluorescence staining, immunostaining, and electron microscopy, although it is noteworthy that visualization of EETs is greatly changed by sample preparation including the extracellular space of EETotic cells and shear flow. Considering the multiple aspects of biological significance, further study into EETs/EETosis is warranted to give a detailed understanding of the roles played in homeostasis and disease pathogenesis.

Lysophosphatidylserine induces eosinophil extracellular trap formation and degranulation: Implications in severe asthma

BACKGROUND

Recent evidence demonstrates that activated eosinophils undergo a distinct form of lytic cell death, accompanied by formation of DNA-based eosinophil extracellular trap (EET) and degranulation, enhancing inflammatory immune responses in asthmatic airways. We previously showed that human blood eosinophils undergo degranulation in response to lysophosphatidylserine (LysoPS), an inflammatory lipid mediator, and strongly express P2Y10, a LysoPS receptor.

METHODS

We evaluated EET, degranulation, and cell death of eosinophils in response to various concentrations of LysoPS. We also compared responsiveness to LysoPS between eosinophils from severe and nonsevere asthmatics.

RESULTS

Extensive EET formation was elicited from a substantial fraction of stimulated eosinophils in response to 50 μmol/L LysoPS. Analyses for LDH and eosinophil-derived neurotoxin release showed that both lytic cell death and degranulation accompanied EET formation in response to LysoPS. Cytological analyses demonstrated that citrullinated histone 3 was present in the extracellular, filamentous DNA structure embedded with eosinophil granules. The LysoPS-induced EET was independent of ROS production and irrelevant to several signaling pathways examined, but dependent on protein arginine deiminase 4. A low concentration of LysoPS (5 μmol/L) did not induce EET or degranulation, but significantly increased platelet-activating factor-induced degranulation. Eosinophils from severe asthmatics exhibited greater degranulation, but not EET formation, in response to LysoPS (50 μmol/L), than those from nonsevere asthmatics, along with great expression of surface P2Y10.

CONCLUSIONS

We identified a novel function of LysoPS, namely induction of EET in association with cytolysis and degranulation. LysoPS-dependent EET or degranulation plays a potential role in eosinophilic inflammation of severe asthma.

The roles of IL-5 and anti-IL-5 treatment in eosinophilic diseases: Asthma, eosinophilic granulomatosis with polyangiitis, and eosinophilic chronic rhinosinusitis

IL-5 is the most potent activator of eosinophils and is produced by Th2 cells and ILC2s. A role for IL-5 in eosinophil extracellular trap cell death, i.e., a proinflammatory cell death, has also been reported. Mepolizumab and benralizumab are humanized mAbs that target IL-5 and the IL-5 receptor α, respectively, and their therapeutic efficacy for severe asthma has been established. Although consistent differences in the efficacies of those drugs have not been proven, benralizumab extensively depleted eosinophils via Ab-dependent cell-mediated cytotoxicity. Blood eosinophil count, but not FeNO or IgE, is the best-established predictive biomarker of the efficacy of anti-IL-5 treatment. Regarding the choice of biologics, the balance between blood eosinophil count and FeNO, indication of comorbidities, longitudinal safety, and interval of injection should be considered. Mepolizumab was also effective in maintaining the remission of refractory eosinophilic granulomatous polyangiitis. Moreover, mepolizumab decreased the proportion of patients who required surgery and lowered the nasal polyp score in patients with chronic rhinosinusitis with nasal polyps; a further extensive trial is currently under way. In a phase II benralizumab study performed in Japan, no significant effect on nasal polyp score at week 12 was observed, suggesting a requirement for longer treatment. In this review, the role of IL-5 in eosinophil biology and the current status of anti-IL-5 therapy are discussed. The longitudinal safety of anti-IL-5 therapy has been increasingly established, and this strategy will be continuously indicated for eosinophilic diseases as a specific treatment for eosinophilic inflammation.

Cellular Stress and General Pathological Processes

From the viewpoint of the general pathology, most of the human diseases are associated with a limited number of pathogenic processes such as inflammation, tumor growth, thrombosis, necrosis, fibrosis, atrophy, pathological hypertrophy, dysplasia and metaplasia. The phenomenon of chronic low-grade inflammation could be attributed to non-classical forms of inflammation, which include many neurodegenerative processes, pathological variants of insulin resistance, atherosclerosis, and other manifestations of the endothelial dysfunction. Individual and universal manifestations of cellular stress could be considered as a basic element of all these pathologies, which has both physiological and pathophysiological significance. The review examines the causes, main phenomena, developmental directions and outcomes of cellular stress using a phylogenetically conservative set of genes and their activation pathways, as well as tissue stress and its role in inflammatory and para-inflammatory processes. The main ways towards the realization of cellular stress and its functional blocks were outlined. The main stages of tissue stress and the classification of its typical manifestations, as well as its participation in the development of the classical and non-classical variants of the inflammatory process, were also described. The mechanisms of cellular and tissue stress are structured into the complex systems, which include networks that enable the exchange of information with multidirectional signaling pathways which together make these systems internally contradictory, and the result of their effects is often unpredictable. However, the possible solutions require new theoretical and methodological approaches, one of which includes the transition to integral criteria, which plausibly reflect the holistic image of these processes.

How Do Innate Immune Cells Contribute to Airway Remodeling in COPD Progression?

Recently, the therapeutic potential of immune-modulation during the progression of chronic obstructive pulmonary disease (COPD) has been attracting increasing interest. However, chronic inflammatory response has been over-simplified in descriptions of the mechanism of COPD progression. As a form of first-line airway defense, epithelial cells exhibit phenotypic alteration, and participate in epithelial layer disorganization, mucus hypersecretion, and extracellular matrix deposition. Dendritic cells (DCs) exhibit attenuated antigen-presenting capacity in patients with advanced COPD. Immature DCs migrate into small airways, where they promote a pro-inflammatory microenvironment and bacterial colonization. In response to damage-associated molecular patterns (DAMPs) in lung tissue affected by COPD, neutrophils are excessively recruited and activated, where they promote a proteolytic microenvironment and fibrotic repair in small airways. Macrophages exhibit decreased phagocytosis in the large airways, while they demonstrate high pro-inflammatory potential in the small airways, and mediate alveolar destruction and chronic airway inflammation. Natural killer T (NKT) cells, eosinophils, and mast cells also play supplementary roles in COPD progression; however, their cellular activities are not yet entirely clear. Overall, during COPD progression, “exhausted” innate immune responses can be observed in the large airways. On the other hand, the innate immune response is enhanced in the small airways. Approaches that inhibit the inflammatory cascade, chemotaxis, or the activation of inflammatory cells could possibly delay the progression of airway remodeling in COPD, and may thus have potential clinical significance.

Eosinophils in the gastrointestinal tract and their role in the pathogenesis of major colorectal disorders

Eosinophils are currently regarded as versatile mobile cells controlling and regulating multiple biological pathways and responses in health and disease. These cells store in their specific granules numerous biologically active substances (cytotoxic cationic proteins, cytokines, growth factors, chemokines, enzymes) ready for rapid release. The human gut is the main destination of eosinophils that are produced and matured in the bone marrow and then transferred to target tissues through the circulation. In health the most important functions of gut-residing eosinophils comprise their participation in the maintenance of the protective mucosal barrier and interactions with other immune cells in providing immunity to microbiota of the gut lumen. Eosinophils are closely involved in the development of inflammatory bowel disease (IBD), when their cytotoxic granule proteins cause damage to host tissues. However, their roles in Crohn’s disease and ulcerative colitis appear to follow different immune response patterns. Eosinophils in IBD are especially important in altering the structure and protective functions of the mucosal barrier and modulating massive neutrophil influx to the lamina propria followed by transepithelial migration to colorectal mucus. IBD-associated inflammatory process involving eosinophils then appears to expand to the mucus overlaying the internal gut surface. The author hypothesises that immune responses within colorectal mucus as well as ETosis exerted by both neutrophils and eosinophils on the both sides of the colonic epithelial barrier act as additional pathogenetic factors in IBD. Literature analysis also shows an association between elevated eosinophil levels and better colorectal cancer (CRC) prognosis, but mechanisms behind this effect remain to be elucidated. In conclusion, the author emphasises the importance of investigating colorectal mucus in IBD and CRC patients as a previously unexplored milieu of disease-related inflammatory responses.

Charcot-Leyden Crystals in Eosinophilic Inflammation: Active Cytolysis Leads to Crystal Formation

PURPOSE OF REVIEW

Charcot-Leyden crystals (CLCs), slender bipyramidal hexagonal crystals, were first described by Jean-Martin Charcot in 1853, predating Paul Ehrlich's "discovery" of eosinophils by 26 years. To date, CLCs are known as a classical hallmark of eosinophilic inflammation. CLC protein expresses palmitate cleaving lysophospholipase activity and is a member of the family of S-type lectins, galectin-10. We summarize current knowledge regarding the pathological observations of CLCs and their mechanism of generation focusing on eosinophil cell death.

RECENT FINDINGS

The presence of CLCs in vivo has been consistently associated with lytic eosinophils. Recent evidence revealed that cytolysis represents the occurrence of extracellular trap cell death (ETosis), an active non-apoptotic cell death process releasing filamentous chromatin structure. Galectin-10 is a predominant protein present within the cytoplasm of eosinophils but not stored in secretory granules. Activated eosinophils undergo ETosis and loss of galectin-10 cytoplasmic localization results in intracellular CLC formation. Free galectin-10 released following plasma membrane disintegration forms extracellular CLCs. Of interest, galectin-10-containing extracellular vesicles are also released during ETosis. Mice models indicated that CLCs could be a novel therapeutic target for Th2-type airway inflammation. The concept of ETosis, which represents a major fate of activated eosinophils, expands our current understanding by which cytoplasmic galectin-10 is crystalized/externalized. Besides CLCs and free galectin-10, cell-free granules, extracellular chromatin traps, extracellular vesicles, and other alarmins, all released through the process of ETosis, have novel implications in various eosinophilic disorders.

Eosinophil Extracellular Traps and Inflammatory Pathologies-Untangling the Web!

Eosinophils are an enigmatic white blood cell, whose immune functions are still under intense investigation. Classically, the eosinophil was considered to fulfill a protective role against parasitic infections, primarily large multicellular helminths. Although eosinophils are predominantly associated with parasite infections, evidence of a role for eosinophils in mediating immunity against bacterial, viral, and fungal infections has been recently reported. Among the mechanisms by which eosinophils are proposed to exert their protective effects is the production of DNA-based extracellular traps (ETs). Remarkably, DNA serves a role that extends beyond its biochemical function in encoding RNA and protein sequences; it is also a highly effective substance for entrapment of bacteria and other extracellular pathogens, and serves as valuable scaffolding for antimicrobial mediators such as granule proteins from immune cells. Extracellular trap formation from eosinophils appears to fulfill an important immune response against extracellular pathogens, although overproduction of traps is evident in pathologies. Here, we discuss the discovery and characterization of eosinophil extracellular traps (EETs) in response to a variety of stimuli, and suggest a role for these structures in the pathogenesis of disease as well as the establishment of autoimmunity in chronic, unresolved inflammation.

Characterization and implications of the dynamics of eosinophils in blood and in the infarcted myocardium after coronary reperfusion

Objective

We characterized the dynamics of eosinophils in blood and in the infarcted myocardium in patients and in a swine model of reperfused myocardial infarction (MI). The association of eosinophil dynamics with various outcomes was assessed.

Methods

Serial eosinophil count and pre-discharge cardiac magnetic resonance were carried out in a prospective series of 620 patients with a first ST-elevation MI. In a swine model of reperfused MI, the dynamics of circulating eosinophils and their presence in the infarcted myocardium were determined. In autopsies from chronic MI patients, eosinophils were quantified.

Results

Patient eosinophil count sharply decreased 12h post-reperfusion compared to arrival. A lower minimum eosinophil count was associated with more extensive edema, microvascular obstruction, and infarct size as measured by cardiac magnetic resonance, and also with a higher rate of cardiac events (death, re-infarction, or heart failure) during follow-up. In the experimental model, eosinophil count boosted during ischemia and dropped back immediately post-reperfusion. Myocardial samples revealed progressive eosinophil migration into the infarcted myocardium, especially areas with microvascular obstruction. Markers of eosinophil maturation and survival (interleukin-5), degranulation (eosinophil cationic protein) and migration (eotoxin-1) were detected in the blood of patients, and in porcine myocardium. Eosinophil infiltration was detected in autopsies from chronic MI patients.

Conclusion

Eosinopenia post-MI was associated with an impaired cardiac structure and adverse events. The decay in circulating eosinophils soon after reperfusion mirrors their migration into the infarcted myocardium, as reflected by their presence in heart samples from swine and patients. Further studies are needed to understanding this unexplored pathway and its therapeutic implications.

Cell death at the cross roads of host-pathogen interaction in Mycobacterium tuberculosis infection

Tuberculosis (TB) continues to be the leading cause of death by any single infectious agent, accounting for around 1.7 million annual deaths globally, despite several interventions and support programs by national and international agencies. With the development of drug resistance in Mycobacterium tuberculosis (M. tb), there has been a paradigm shift in TB research towards host-directed therapy. The potential targets include the interactions between host and bacterial proteins that are crucial for pathogenesis. Hence, collective efforts are being made to understand the molecular details of host-pathogen interaction for possible translation into host-directed therapy. The present review focuses on 'host cell death modalities' of host-pathogen interaction, which play a crucial role in determining the outcome of TB disease progression. Several cell death modalities that occur in response to mycobacterial infection have been identified in human macrophages either as host defences for bacterial clearance or as pathogen strategies for multiplication and dissemination. These cell death modalities include apoptosis, necrosis, pyroptosis, necroptosis, pyronecrosis, NETosis, and autophagy. These processes are highly overlapping with several mycobacterial proteins participating in more than one cell death pathway. Until now, reviews in M. tb and host cell death have discussed either focusing on host evasion strategies, apoptosis, autophagy, and necrosis or describing all these forms with limited discussions of their role in host-pathogen interactions. Here, we present a comprehensive review of various mycobacterial factors modulating host cell death pathways and the cross-talk between them. Besides this, we have discussed the networking of host cell death pathways including the interference of host miRNA during M. tb infection with their respective targets. Through this review, we present the host targets that overlap across several cell death modalities and the technical limitations of methodology in cell death research. Given the compelling need to discover alternative drug target(s), this review identifies these overlapping cell death factors as potential targets for host-directed therapy.

β2 -Adrenoceptors inhibit neutrophil extracellular traps in human polymorphonuclear leukocytes

This study tests the hypothesis that in isolated human polymorphonuclear leukocytes (PMN) adrenergic ligands can affect neutrophil extracellular trap (NET) formation. We have previously shown that, in PMN, adrenaline (A), through the activation of adrenergic receptors (AR), reduces stimulus-dependent cell activation; we have, therefore, planned to investigate if AR are involved in NET production. PMN were obtained from venous blood of healthy subject. The ability of adrenergic ligands to affect reactive oxygen species (ROS) production, NET production, and cell migration was investigated in cells cultured under resting conditions or after activation with N-formyl-methionyl-leucyl-phenylalanine (fMLP), LPS, or IL-8. Stimuli-induced NET production measured as ROS, microscopic evaluation, and elastase production was reverted by A and this effect was blocked by the selective β₂ -AR antagonist ICI-118,551. The stimulus-induced ROS generation and migration was prevented by A and by isoprenaline (ISO), and these effects were counteracted only by ICI-118,551 and not by the other two selective ligands for the β₁ and β₃ -AR. Finally, the presence of the β-ARs on PMN was confirmed, by means of microscopy and flow cytometry. The data of the present study suggest that adrenergic compounds, through the interaction of mainly β₂ -AR, are able to affect neutrophil functions. These data are suggestive of a possible therapeutic role of β₂ -AR ligands (in addition to their classical use), promoting the possible therapeutic relevance of adrenergic system in the modulation of innate immunity proposing their possible use as anti-inflammatory drugs.

Therapeutic use of heparin and derivatives beyond anticoagulation in patients with bronchial asthma or COPD

In this review, we identify potential targets for the therapeutic effects of heparin in asthma and chronic obstructive pulmonary disease (COPD), consider the safety and delivery modalities of this therapeutic approach. Specifically, we point to the anti-inflammatory, antioxidant and mucolytic effects of unfractionated heparin with potential to modify disease progression in COPD and asthma when administered via the inhaled route. Inhaled heparin may represent an effective add-on therapy in COPD and asthma patient groups, especially when taking into consideration the relative deficiency in endogenous heparin reported in asthma patients.