Linking adipose tissue eosinophils, IL-4, and leptin in human obesity and insulin resistance

BACKGROUNDObesity is a multifactorial disease with adverse health implications including insulin resistance (IR). In patients with obesity, the presence of high circulating levels of leptin, deemed hyperleptinemia, is associated with IR. Recent data in mice with diet-induced obesity (DIO) show that a partial reduction in leptin levels improves IR. Additional animal studies demonstrate that IL-4 decreases leptin levels. In rodents, resident adipose tissue eosinophils (AT-EOS) are the main source of IL-4 and are instrumental in maintaining metabolic homeostasis. A marked reduction in AT-EOS content is observed in animal models of DIO. These observations have not been explored in humans.METHODSWe analyzed AT from individuals with obesity and age-matched lean counterparts for AT-EOS content, IL-4, circulating leptin levels, and measures of IR.RESULTSOur results show that individuals with obesity (n = 15) had a significant reduction in AT-EOS content (P < 0.01), decreased AT-IL-4 gene expression (P = 0.02), and decreased IL-4 plasma levels (P < 0.05) in addition to expected IR (P < 0.001) and hyperleptinemia (P < 0.01) compared with lean subjects (n = 15). AT-EOS content inversely correlated with BMI (P = 0.002) and IR (P = 0.005). Ex vivo AT explants and in vitro cell culture of primary human mature adipocytes exposed to either IL-4 or EOS conditioned media produced less leptin (P < 0.05).CONCLUSIONOur results suggest that IL-4 acts as a link between EOS, AT, and leptin production. Future studies exploring this interaction may identify an avenue for the treatment of obesity and its complications through amelioration of hyperleptinemia.TRIAL REGISTRATIONClinicaltrials.gov NCT02378077 & NCT04234295.

Eosinophils restrain humoral alloimmunity after lung transplantation

While the function of many leukocytes in transplant biology has been well defined, the role of eosinophils is controversial and remains poorly explored. Conflicting data exist regarding eosinophils' role in alloimmunity. Due to their prevalence in the lung, and their defined role in other pulmonary pathologies such as asthma, we set out to explore the role of eosinophils in the long-term maintenance of the lung allograft. We noted that depletion of eosinophils results in the generation of donor-specific antibodies. Eosinophil depletion increased memory B cell, plasma cell, and antibody-secreting cell differentiation and resulted in de novo generation of follicular germinal centers. Germinal center formation depended on the expansion of CD4+Foxp3-Bcl6+CXCR5+PD-1+ T follicular helper (Tfh) cells, which increase in number after eosinophil depletion. Mechanistically, we demonstrate that eosinophils prevent Tfh cell generation by acting as the dominant source of IFN-γ in an established lung allograft, thus facilitating Th1 rather than Tfh polarization of naive CD4+ T cells. Our data thus describe what we believe is a unique and previously unknown role for eosinophils in maintaining allograft tolerance and suggest that indiscriminate administration of eosinophil-lytic corticosteroids for treatment of acute cellular rejection may inadvertently promote humoral alloimmunity.

Staphylococcus aureus proteases trigger eosinophil-mediated skin inflammation

Staphylococcus aureus skin colonization and eosinophil infiltration are associated with many inflammatory skin disorders, including atopic dermatitis, bullous pemphigoid, Netherton's syndrome, and prurigo nodularis. However, whether there is a relationship between S. aureus and eosinophils and how this interaction influences skin inflammation is largely undefined. We show in a preclinical mouse model that S. aureus epicutaneous exposure induced eosinophil-recruiting chemokines and eosinophil infiltration into the skin. Remarkably, we found that eosinophils had a comparable contribution to the skin inflammation as T cells, in a manner dependent on eosinophil-derived IL-17A and IL-17F production. Importantly, IL-36R signaling induced CCL7-mediated eosinophil recruitment to the inflamed skin. Last, S. aureus proteases induced IL-36α expression in keratinocytes, which promoted infiltration of IL-17-producing eosinophils. Collectively, we uncovered a mechanism for S. aureus proteases to trigger eosinophil-mediated skin inflammation, which has implications in the pathogenesis of inflammatory skin diseases.

A Simple Cuff Technique for Murine Left Lung Transplantation

Over the past decade, our laboratory has made significant progress in developing and refining vascularized mouse lung transplantation models using an efficient and highly reliable "cuff technique" of transplantation. This article describes a sophisticated and comprehensive method for orthotopic lung transplantation in a vascularized orthotopic lung model, representing the most physiologic and clinically relevant model of mouse lung transplantation to date. The transplantation process consists of two distinct stages: donor harvest and subsequent implantation into the recipient. The method has been successfully mastered, and with several months of sufficient training, a skilled practitioner can perform the procedure in approximately 90 min from skin-to-skin. Surprisingly, once individuals overcome the initial learning curve, the survival rate during the perioperative period approaches nearly 100%. The mouse model allows for the use of multiple commercially available transgenic and mutant strains of mice, enabling the study of tolerance and rejection. Additionally, the unique features of this model make it a valuable tool for investigating tumor biology and immunology.

Eosinophil Peroxidase: A Biomarker for Eosinophilic Chronic Rhinosinusitis Agnostic of Polyp Status

OBJECTIVE

To evaluate eosinophil peroxidase (EPX) as a biomarker for tissue levels of eosinophilia, cytokines, and chemokines within chronic rhinosinusitis (CRS).

METHODS

Twenty-eight subjects undergoing sinonasal surgery were prospectively enrolled. Ethmoid tissue was analyzed with an in-house EPX immunoassay and a 48-plex cytokine-chemokine array. Clinical severity was assessed using SNOT-22 and Lund-Mackay scores. Subjects were grouped as follows: controls, polyp status (CRS with [CRSwNP] and without nasal polyps [CRSsNP]), tissue eosinophilia (eosinophilic CRS [eCRS], non-eosinophilic CRS [neCRS]), or combinations thereof (eCRSwNP, eCRSsNP, neCRSsNP). eCRS was defined as >10 eosinophils per high power field (HPF). Subjects without CRS or asthma were enrolled as controls.

RESULTS

EPX was elevated in CRSwNP compared to control (p = 0.007), in eCRS compared to neCRS (p = 0.002), and in eCRSwNP along with eCRSsNP compared to neCRSsNP (p = 0.023, p = 0.015, respectively). eCRS displayed elevated IL-5 compared to neCRS (p = 0.005). No significant differences in EPX or IL-5 were observed between eCRSwNP and eCRSsNP. IL-5 was elevated in eCRSwNP (p = 0.019) compared neCRSsNP. Area under the receiver operator characteristic curve was 0.938 (95% CI, 0.835-1.00) for EPX and tissue eosinophilia, with an optimal cut-point of 470 ng/mL being 100% specific and 81.25% sensitive for tissue eosinophilia. Linear regression revealed a strong correlation between EPX and IL-5 (R2  = 0.64, p < 0.001). Comparing EPX and IL-5, only EPX displayed significant correlation with SNOT-22 (p = 0.04) and Lund-Mackay score (p = 0.004).

CONCLUSION

EPX is associated with tissue eosinophilia in CRS patients regardless of polyp status. EPX correlates with IL-5 and could be potentially considered a biomarker for anti-IL-5 therapies.

LEVEL OF EVIDENCE

3 Laryngoscope, 134:69-78, 2024.

Safety and Efficacy of Dexpramipexole in Eosinophilic Asthma (EXHALE): A randomized controlled trial

BACKGROUND

There is a need for new and effective oral asthma therapies. Dexpramipexole, an oral eosinophil-lowering drug, has not previously been studied in asthma.

OBJECTIVE

We sought to evaluate the safety and efficacy of dexpramipexole in lowering blood and airway eosinophilia in subjects with eosinophilic asthma.

METHODS

We performed a randomized, double-blind, placebo-controlled proof-of-concept trial in adults with inadequately controlled moderate to severe asthma and blood absolute eosinophil count (AEC) greater than or equal to 300/μL. Subjects were randomly assigned (1:1:1:1) to dexpramipexole 37.5, 75, or 150 mg BID (twice-daily) or placebo. The primary end point was the relative change in AEC from baseline to week 12. Prebronchodilator FEV1 week-12 change from baseline was a key secondary end point. Nasal eosinophil peroxidase was an exploratory end point.

RESULTS

A total of 103 subjects were randomly assigned to dexpramipexole 37.5 mg BID (N = 22), 75 mg BID (N = 26), 150 mg BID (N = 28), or placebo (N = 27). Dexpramipexole significantly reduced placebo-corrected AEC week-12 ratio to baseline, in both the 150-mg BID (ratio, 0.23; 95% CI, 0.12-0.43; P < .0001) and the 75-mg BID (ratio, 0.34; 95% CI, 0.18-0.65; P = .0014) dose groups, corresponding to 77% and 66% reductions, respectively. Dexpramipexole reduced the exploratory end point of nasal eosinophil peroxidase week-12 ratio to baseline in the 150-mg BID (median, 0.11; P = .020) and the 75-mg BID (median, 0.17; P = .021) groups. Placebo-corrected FEV1 increases were observed starting at week 4 (nonsignificant). Dexpramipexole displayed a favorable safety profile.

CONCLUSIONS

Dexpramipexole demonstrated effective eosinophil lowering and was well tolerated. Additional larger clinical trials are needed to understand the clinical efficacy of dexpramipexole in asthma.

Eosinophils promote effector functions of lung group 2 innate lymphoid cells in allergic airway inflammation in mice

BACKGROUND

Group 2 innate lymphoid cells (ILC2s) are critical mediators of type 2 respiratory inflammation, releasing IL-5 and IL-13 and promoting the pulmonary eosinophilia associated with allergen provocation. Although ILC2s have been shown to promote eosinophil activities, the role of eosinophils in group 2 innate lymphoid cell (ILC2) responses is less well defined.

OBJECTIVE

We sought to investigate the role of eosinophils in activation of ILC2s in models of allergic asthma and in vitro.

METHODS

Inducible eosinophil-deficient mice were exposed to allergic respiratory inflammation models of asthma, such as ovalbumin or house dust mite challenge, or to innate models of type 2 airway inflammation, such as inhalation of IL-33. Eosinophil-specific IL-4/13-deficient mice were used to address the specific roles for eosinophil-derived cytokines. Direct cell interactions between ILC2s and eosinophils were assessed by in vitro culture experiments.

RESULTS

Targeted depletion of eosinophils resulted in significant reductions of total and IL-5+ and IL-13+ lung ILC2s in all models of respiratory inflammation. This correlated with reductions in IL-13 levels and mucus in the airway. Eosinophil-derived IL-4/13 was necessary for both eosinophil and ILC2 accumulation in lung in allergen models. In vitro, eosinophils released soluble mediators that induced ILC2 proliferation and G protein-coupled receptor-dependent chemotaxis of ILC2s. Coculture of ILC2s and IL-33-activated eosinophils resulted in transcriptome changes in both ILC2s and eosinophils, suggesting potential novel reciprocal interactions.

CONCLUSION

These studies demonstrate that eosinophils play a reciprocal role in ILC2 effector functions as part of both adaptive and innate type 2 pulmonary inflammatory events.

Eosinophils protect against acetaminophen-induced liver injury through cyclooxygenase-mediated IL-4/IL-13 production

BACKGROUND AND AIMS

A better understanding of the underlying mechanism of acetaminophen (APAP)-induced liver injury (AILI) remains an important endeavor to develop therapeutic approaches. Eosinophils have been detected in liver biopsies of patients with APAP overdose. We recently demonstrated a profound protective role of eosinophils against AILI; however, the molecular mechanism had not been elucidated.

APPROACH AND RESULTS

In agreement with our previous data from experiments using genetic deletion of eosinophils, we found that depletion of eosinophils in wild-type (WT) mice by an anti-IL-15 antibody resulted in exacerbated AILI. Moreover, adoptive transfer of eosinophils significantly reduced liver injury and mortality rate in WT mice. Mechanistic studies using eosinophil-specific IL-4/IL-13 knockout mice demonstrated that these cytokines, through inhibiting interferon-γ, mediated the hepatoprotective function of eosinophils. Reverse phase protein array analyses and in vitro experiments using various inhibitors demonstrated that IL-33 stimulation of eosinophils activated p38 mitogen-activated protein kinase (MAPK), and in turn, cyclooxygenases (COX), which triggered NF-κB-mediated IL-4/IL-13 production. In vivo adoptive transfer experiments showed that in contrast to naive eosinophils, those pretreated with COX inhibitors failed to attenuate AILI.

CONCLUSIONS

The current study revealed that eosinophil-derived IL-4/IL-13 accounted for the hepatoprotective effect of eosinophils during AILI. The data demonstrated that the p38 MAPK/COX/NF-κB signaling cascade played a critical role in inducing IL-4/IL-13 production by eosinophils in response to IL-33.

Solving the Conundrum of Eosinophils in Alloimmunity

Eosinophils are bone-marrow-derived granulocytes known for their ability to facilitate clearance of parasitic infections and their association with asthma and other inflammatory diseases. The purpose of this review is to discuss the currently available human observational and animal experimental data linking eosinophils to the immunologic response in solid organ transplantation. First, we present observational human studies that demonstrate a link between transplantation and eosinophils yet were unable to define the exact role of this cell population. Next, we describe published experimental models and demonstrate a defined mechanistic role of eosinophils in downregulating the alloimmune response to murine lung transplants. The overall summary of this data suggests that further studies are needed to define the role of eosinophils in multiple solid organ allografts and points to the possibility of manipulating this cell population to improve graft survival.

Hepatic recruitment of eosinophils and their protective function during acute liver injury

BACKGROUND & AIMS

Beyond the classical description of eosinophil functions in parasite infections and allergic diseases, emerging evidence supports a critical role of eosinophils in resolving inflammation and promoting tissue remodeling. However, the role of eosinophils in liver injury and the underlying mechanism of their recruitment into the liver remain unclear.

METHODS

Hepatic eosinophils were detected and quantified using flow cytometry and immunohistochemical staining. Eosinophil-deficient (ΔdblGata1) mice were used to investigate the role of eosinophils in 3 models of acute liver injury. In vivo experiments using Il33-/- mice and macrophage-depleted mice, as well as in vitro cultures of eosinophils and macrophages, were performed to interrogate the mechanism of eotaxin-2 (CCL24) production.

RESULTS

Hepatic accumulation of eosinophils was observed in patients with acetaminophen (APAP)-induced liver failure, whereas few eosinophils were detectable in healthy liver tissues. In mice treated with APAP, carbon tetrachloride or concanavalin A, eosinophils were recruited into the liver and played a profound protective role. Mice deficient of macrophages or IL-33 exhibited impaired hepatic eosinophil recruitment during acute liver injury. CCL24, but not CCL11, was increased after treatment of each hepatotoxin in an IL-33 and macrophage-dependent manner. In vitro experiments demonstrated that IL-33, by stimulating IL-4 release from eosinophils, promoted the production of CCL24 by macrophages.

CONCLUSIONS

This is the first study to demonstrate that hepatic recruitment of and protection by eosinophils occur commonly in various models of acute liver injury. Our findings support further exploration of eosinophils as a therapeutic target to treat APAP-induced acute liver injury.

LAY SUMMARY

The current study unveils that eosinophils are recruited into the liver and play a protective function during acute liver injury caused by acetaminophen overdose. The data demonstrate that IL-33-activated eosinophils trigger macrophages to release high amounts of CCL24, which promotes hepatic eosinophil recruitment. Our findings suggest that eosinophils could be an effective cell-based therapy for the treatment of acetaminophen-induced acute liver injury.

The aryl hydrocarbon receptor instructs the immunomodulatory profile of a subset of Clec4a4+ eosinophils unique to the small intestine

C-type lectin domain family 4, member a4 (Clec4a4) is a C-type lectin inhibitory receptor specific for glycans thought to be exclusively expressed on murine CD8α− conventional dendritic cells. Using newly generated Clec4a4-mCherry knock-in mice, we identify a subset of Clec4a4-expressing eosinophils uniquely localized in the small intestine lamina propria. Clec4a4+ eosinophils evinced an immunomodulatory signature, whereas Clec4a4− eosinophils manifested a proinflammatory profile. Clec4a4+ eosinophils expressed high levels of aryl hydrocarbon receptor (Ahr), which drove the expression of Clec4a4 as well as other immunomodulatory features, such as PD-L1. The abundance of Clec4a4+ eosinophils was dependent on dietary AHR ligands, increased with aging, and declined in inflammatory conditions. Mice lacking AHR in eosinophils expanded innate lymphoid cells of type 2 and cleared Nippostrongylus brasiliensis infection more effectively than did wild-type mice. These results highlight the heterogeneity of eosinophils in response to tissue cues and identify a unique AHR-dependent subset of eosinophils in the small intestine with an immunomodulatory profile.

MR1-dependent immune surveillance of the skin contributes to pathogenesis and is a photobiological target of UV light therapy in a mouse model of atopic dermatitis

BACKGROUND

Mucosal-associated invariant T (MAIT) cells are unconventional T cells which recognize microbial metabolites presented by the major histocompatibility complex class I-related molecule MR1. Although MAIT cells have been shown to reside in human and murine skin, their contribution to atopic dermatitis (AD), an inflammatory skin disease associated with barrier dysfunction and microbial translocation, has not yet been determined.

METHODS

Genetic deletion of MR1 and topical treatment with inhibitory MR1 ligands, which result in the absence and functional inhibition of MAIT cells, respectively, were used to investigate the role of MR1-dependent immune surveillance in a MC903-driven murine model of AD.

RESULTS

The absence or inhibition of MR1 arrested AD disease progression through the blockade of both eosinophil activation and recruitment of IL-4- and IL-13-producing cells. In addition, the therapeutic efficacy of phototherapy against MC903-driven AD could be increased with prior application of folate, which photodegrades into the inhibitory MR1 ligand 6-formylpterin.

CONCLUSION

We identified MAIT cells as sentinels and mediators of cutaneous type 2 immunity. Their pathogenic activity can be inhibited by topical application or endogenous generation, via phototherapy, of inhibitory MR1 ligands.

Thymic stromal lymphopoietin induces adipose loss through sebum hypersecretion

Emerging studies indicate that the immune system can regulate systemic metabolism. Here, we show that thymic stromal lymphopoietin (TSLP) stimulates T cells to induce selective white adipose loss, which protects against obesity, improves glucose metabolism, and mitigates nonalcoholic steatohepatitis. Unexpectedly, adipose loss was not caused by alterations in food intake, absorption, or energy expenditure. Rather, it was induced by the excessive loss of lipids through the skin as sebum. TSLP and T cells regulated sebum release and sebum-associated antimicrobial peptide expression in the steady state. In human skin, TSLP expression correlated directly with sebum-associated gene expression. Thus, we establish a paradigm in which adipose loss can be achieved by means of sebum hypersecretion and uncover a role for adaptive immunity in skin barrier function through sebum secretion.

Gastrointestinal Eosinophil Responses in a Longitudinal, Randomized Trial of Peanut Oral Immunotherapy

BACKGROUND & AIMS

Gastrointestinal side effects are common during oral immunotherapy (OIT) and eosinophilic esophagitis (EoE) is a potential complication. We aimed to characterize eosinophilic gastrointestinal responses to peanut OIT, in which peanut protein is given orally, with incremental increases in dose over time.

METHODS

Twenty adults with IgE-mediated peanut allergy were randomly assigned to groups given peanut OIT (n = 15) or placebo (n = 5); 1 additional subject withdrew before randomization. Serial gastrointestinal biopsies were collected at baseline (n = 21, 0 weeks), following dose escalation (n = 10, 52 weeks), and during the maintenance phase (n = 11, 104 weeks). Endoscopic findings were characterized using the EoE endoscopic reference score. Biopsies were assessed for eosinophils per high-power field (eos/hpf) and other pathology features using EoE histologic scoring system scores. We performed immunohistochemical analyses of eosinophil peroxidase deposition, quantified using automated image analysis.

RESULTS

At baseline, no subjects reported current gastrointestinal symptoms. However, 3 of the 21 subjects (14%) had esophageal peak eosinophil counts ≥15 eos/hpf and all subjects had dilated intercellular spaces (DIS). OIT induced or exacerbated esophageal eosinophilia (EE) at 52 weeks in most subjects (peak eosinophil counts >5 eos/hpf in 6 of 7 patients [86%]; peak eosinophil counts ≥15 eos/hpf in 4 of 7 patients [57%]). One subject met clinicopathologic criteria for EoE and withdrew; no significant changes in esophageal peak eosinophil counts were observed in the placebo group. EE in the OIT group corresponded with significant increases in EoE histologic scoring system scores and deposition of eosinophil peroxidase. In 4 of 6 participants (67%), OIT-induced EE and gastrointestinal eosinophilia resolved by the end of the maintenance phase. Gastrointestinal symptoms were not clearly associated with EE or gastrointestinal eosinophilia.

CONCLUSIONS

In this pilot study, we found that peanut OIT-induced EE and gastrointestinal eosinophilia are usually transient and are not always associated with gastrointestinal symptoms. Clinicaltrials.gov no: NCT02103270.

Eosinophil Knockout Humans: Uncovering the Role of Eosinophils Through Eosinophil-Directed Biological Therapies

The enigmatic eosinophil has emerged as an exciting component of the immune system, involved in a plethora of homeostatic and inflammatory responses. Substantial progress has been achieved through experimental systems manipulating eosinophils in vivo, initially in mice and more recently in humans. Researchers using eosinophil knockout mice have identified a contributory role for eosinophils in basal and inflammatory processes and protective immunity. Primarily fueled by the purported proinflammatory role of eosinophils in eosinophil-associated diseases, a series of anti-eosinophil therapeutics have emerged as a new class of drugs. These agents, which dramatically deplete eosinophils, provide a valuable opportunity to characterize the consequences of eosinophil knockout humans. Herein, we comparatively describe mouse and human eosinophil knockouts. We put forth the view that human eosinophils negatively contribute to a variety of diseases and, unlike mouse eosinophils, do not yet have an identified role in physiological health; thus, clarifying all roles of eosinophils remains an ongoing pursuit.

Eosinophils attenuate hepatic ischemia-reperfusion injury in mice through ST2-dependent IL-13 production

Eosinophils are a myeloid cell subpopulation that mediates type 2 T helper cell immune responses. Unexpectedly, we identified a rapid accumulation of eosinophils in 22 human liver grafts after hepatic transplantation. In contrast, no eosinophils were detectable in healthy liver tissues before transplantation. Studies with two genetic mouse models of eosinophil deficiency and a mouse model of antibody-mediated eosinophil depletion revealed exacerbated liver injury after hepatic ischemia and reperfusion. Adoptive transfer of bone marrow-derived eosinophils normalized liver injury of eosinophil-deficient mice and reduced hepatic ischemia and reperfusion injury in wild-type mice. Mechanistic studies combining genetic and adoptive transfer approaches identified a critical role of suppression of tumorigenicity (ST2)-dependent production of interleukin-13 by eosinophils in the hepatoprotection against ischemia-reperfusion-induced injury. Together, these data provide insight into a mechanism of eosinophil-mediated liver protection that could serve as a therapeutic target to improve outcomes of patients undergoing liver transplantation.

Assessment of Lung Eosinophils In Situ Using Immunohistological Staining

Eosinophils are rare white blood cells that are recruited from circulation to accumulate in the lung in mouse models of allergic respiratory inflammation. In hematoxylin-eosin (HE) stained lungs, eosinophils may be difficult to detect despite their bright eosin staining in the secondary granules. For this reason, antibody-mediated detection of eosinophils is preferable for specific and clearer identification of these cells. Moreover, eosinophils may degranulate, releasing their granule proteins into surrounding tissue, and remnants of cytolysed cells cannot be detected by HE staining. The methods here demonstrate the use of eosinophil-specific anti-mouse antibodies to detect eosinophil granule proteins in formalin-fixed cells both in situ in paraffin-embedded lungs, as well as in cytospin preparations from the lung. These antibody staining techniques enable either colorimetric or fluorescence imaging of eosinophils or their granule proteins with the potential for additional antibodies to be added for detection of multiple molecules.

M2-like, dermal macrophages are maintained via IL-4/CCL24-mediated cooperative interaction with eosinophils in cutaneous leishmaniasis

Tissue-resident macrophages (TRMs) maintain tissue homeostasis, but they can also provide a replicative niche for intracellular pathogens such as Leishmania How dermal TRMs proliferate and maintain their M2 properties even in the strong T_H1 environment of the L. major infected dermis is not clear. Here, we show that, in infected mice lacking IL-4/13 from eosinophils, dermal TRMs shifted to a proinflammatory state, their numbers declined, and disease was attenuated. Intravital microscopy revealed a rapid infiltration of eosinophils followed by their tight interaction with dermal TRMs. IL-4-stimulated dermal TRMs, in concert with IL-10, produced a large amount of CCL24, which functioned to amplify eosinophil influx and their interaction with dermal TRMs. An intraperitoneal helminth infection model also demonstrated a requirement for eosinophil-derived IL-4 to maintain tissue macrophages through a CCL24-mediated amplification loop. CCL24 secretion was confined to resident macrophages in other tissues, implicating eosinophil-TRM cooperative interactions in diverse inflammatory settings.

Primary tumors from mucosal barrier organs drive unique eosinophil infiltration patterns and clinical associations

Eosinophils are bone marrow-derived granulocytes that display key effector functions in allergic diseases. Nonetheless, recent data highlight important roles for eosinophils in the tumor microenvironment (TME). Eosinophils have been attributed with pleiotropic and perhaps conflicting functions, which may be attributed at least in part to variations in eosinophil quantitation in the TME. Thus, a reliable, quantitative, and robust method for the assessment of eosinophilic infiltration in the TME is required. This type of methodology could standardize the identification of these cells and promote the subsequent generation of hypothesis-driven mechanistic studies. To this end, we conducted a comprehensive analysis of multiple primary tumors from distinct anatomical sites using a standardized method. Bioinformatics analysis of 10,469 genomically profiled primary tumors revealed that eosinophil abundance within different tumors can be categorized into three groups representing tumors with high, intermediate, and low eosinophil levels. Consequently, eosinophil abundance, as well as spatial distribution, was determined in tissue tumor arrays of six tumors representing all three classifications (colon and esophagus - high; lung - intermediate; cervix, ovary, and breast - low). With the exception of breast cancer, eosinophils were mainly localized in the tumor stroma. Importantly, the tumor anatomical site was identified as the primary predictive factor of eosinophil stromal density highlighting a distinction between mucosal-barrier organs versus non-mucosal barrier organs. These findings enhance our understanding of eosinophil diversity in the TME and provide a compelling rationale for future experiments assessing the activity of these cells.

Can eosinophils in adipose tissue add fuel to the fire?

In inguinal adipose tissue, beige adipocytes are interspersed among white adipocytes and in close communication with dynamic populations of immune cells. Recent data have demonstrated that anti-inflammatory macrophages (M2) increase thermogenic activity of beige adipocytes, although the mechanism is currently under debate. ILC2, cells via secretion, of methionine enkephalin peptide were found to be able to increase beige thermogenesis. Knights et al. have recently generated a whole-body knock-out of KLF3 (KLF3-/-) to explore its contribution to thermogenesis and weight gain in a diet-induced obesity animal model.

A FACS-based approach to obtain viable eosinophils from human adipose tissue

Eosinophils have been widely investigated in asthma and allergic diseases. More recently, new insights into the biology of these cells has illustrated eosinophils contribute to homeostatic functions in health such as regulation of adipose tissue glucose metabolism. Human translational studies are limited by the difficulty of obtaining cells taken directly from their tissue environment, relying instead on eosinophils isolated from peripheral blood. Isolation techniques for tissue-derived eosinophils can result in unwanted cell or ribonuclease activation, leading to poor cell viability or RNA quality, which may impair analysis of effector activities of these cells. Here we demonstrate a technique to obtain eosinophils from human adipose tissue samples for the purpose of downstream molecular analysis. From as little as 2 g of intact human adipose tissue, greater than 10⁴ eosinophils were purified by fluorescence-activated cell sorting (FACS) protocol resulting in ≥ 99% purity and ≥ 95% viable eosinophils. We demonstrated that the isolated eosinophils could undergo epigenetic analysis to determine differences in DNA methylation in various settings. Here we focused on comparing eosinophils isolated from human peripheral blood vs human adipose tissue. Our results open the door to future mechanistic investigations to better understand the role of tissue resident eosinophils in different context.

Divergent Siglec-F(eights) of mouse and human eosinophil death

Discussion on the differences between mouse and human eosinophil induced death by antibody ligation to human Siglec-8 and mouse Siglec-F.

OR04-05 MYOD1 Is Associated with Eosinophil-Mediated Browning of Subcutaneous Adipose Tissue

A novel role for adipose tissue (AT)-resident eosinophils (EOS) in metabolism has been suggested. These data were obtained using genetic animal models with either whole-body overexpression of Interleukin-5 (IL-5Tg) leading to eosinophilia or gene ablation resulting in complete lack of EOS. These models limit the specificity of the findings. We hypothesized that AT-resident EOS play a specific role in whole-body metabolism. To this end, we generated a transgenic mouse model overexpressing human eotaxin-2 (hE2) under the control of a fat-specific aP2 promoter, which would exclusively recruit circulating EOS into AT (hEo2Tg), without any changes in the overall EOS numbers. Compared with wild type (WT) mice, AT-EOS numbers were markedly increased in multiple fat depots from hEo2Tg mice, including subcutaneous white adipose tissue (sWAT). After 12 weeks of high-fat diet (HFD), hEo2Tg mice showed significantly less body weight gain and fat mass compared with WT littermates. These changes were associated with an improvement in glucose tolerance. We also found increased oxygen consumption and heat production in hEo2Tg mice under room temperature conditions. The increased thermogenesis was accompanied with an increased expression of browning genes such as Ucp1, Prdm16, Dio2 in sWAT from hEo2Tg HFD mice. So far, our data suggest that AT-resident EOS promote browning of sWAT. This, in turn, protects our animals against development of HFD-induced obesity and insulin resistance. Next, whole transcriptome mRNA sequencing and bioinformatic analyses were performed and showed a significant increase of myogenic differentiation 1 (Myod1) gene expression in hEo2Tg sWAT mice. This was confirmed by qRT-PCR. Myod1 is a key regulator of skeletal muscle differentiation. Given the shared features between brown fat and skeletal muscle, we speculate that by increasing Myod1 gene expression, (AT)-resident EOS mediate sWAT browning. Additional studies are needed to determine the molecular mechanism(s) underling the regulation of Myod1 gene expression by AT-resident EOS and its effect on sWAT browning.

M2-like, dermal macrophages are maintained via IL-4/CCL24 mediated cooperative interaction with eosinophils in cutaneous leishmaniasis

Tissue-resident macrophages (TRMs) maintain tissue homeostasis, but they can also provide a replicative niche for intracellular pathogens such as Leishmania. How dermal TRMs proliferate and maintain their M2 properties even in the strong TH1 environment of the L. major infected dermis is not clear. Here, we show that in infected mice lacking IL-4/IL-13 from eosinophils, dermal TRMs shifted to a pro-inflammatory state, their numbers declined, and disease was attenuated. Intravital microscopy revealed a rapid infiltration of eosinophils followed by their tight interaction with dermal TRMs. IL-4-stimulated dermal TRMs, in concert with IL-10, produced a large amount of CCL24 which functioned to amplify eosinophil influx and their interaction with dermal TRMs. An intraperitoneal helminth infection model also demonstrated a requirement for eosinophil-derived IL-4 to maintain tissue macrophages through a CCL24-mediated amplification loop. CCL24 secretion was confined to resident macrophages in other tissues, implicating eosinophil-TRM cooperative interactions in diverse inflammatory settings.

Deciphering the role of eosinophils in solid organ transplantation

Eosinophils are rare granulocytes that belong to the innate arm of the immune system. This cell population is traditionally defined as a destructive and cytotoxic mediator in asthma and helminth infection. Limited data in transplantation have suggested that eosinophils play a similar role in potentiating deleterious organ inflammation and immunologic rejection. Contrary to this long-held notion, recent data have uncovered the possibility that eosinophils play an alternative role in immune homeostasis, defense against a wide range of pathogens, as well as downregulation of deleterious inflammation. Specifically, translational data from small animal models of lung transplantation have demonstrated a critical role for eosinophils in the downregulation of alloimmunity. These findings shed new light on the unique immunologic features of the lung allograft and demonstrate that environmental polarization may alter the phenotype and function of leukocyte populations previously thought to be static in nature. In this review, we provide an update on eosinophils in the homeostasis of the lung as well as other solid organs.

Intravital imaging of eosinophils: Unwrapping the enigma

Eosinophils are traditionally associated with allergic and parasitic inflammation. More recently, eosinophils have also been shown to have roles in diverse processes including development, intestinal health, thymic selection, and B-cell survival with the majority of these insights being derived from murine models and in vitro assays. Despite this, tools to measure the dynamic activity of eosinophils in situ have been lacking. Intravital microscopy is a powerful tool that enables direct visualization of leukocytes and their dynamic behavior in real-time in a wide range of processes in both health and disease. Until recently eosinophil researchers have not been able to take full advantage of this technology due to a lack of tools such as genetically encoded reporter mice. This mini-review examines the history of intravital microscopy with a focus on eosinophils. The development and use of eosinophil-specific Cre (EoCre) mice to create GFP and tdTomato fluorescent reporter animals is also described. Genetically encoded eosinophil reporter mice combined with intravital microscopy provide a powerful tool to add to the toolbox of technologies that will help us unravel the mysteries still surrounding this cell.

Eosinophils downregulate lung alloimmunity by decreasing TCR signal transduction

Despite the accepted notion that granulocytes play a universally destructive role in organ and tissue grafts, it has been recently described that eosinophils can facilitate immunosuppression-mediated acceptance of murine lung allografts. The mechanism of eosinophil-mediated tolerance, or their role in regulating alloimmune responses in the absence of immunosuppression, remains unknown. Using lung transplants in a fully MHC-mismatched BALB/c (H2d) to C57BL/6 (H2b) strain combination, we demonstrate that eosinophils downregulate T cell-mediated immune responses and play a tolerogenic role even in the absence of immunosuppression. We further show that such downregulation depends on PD-L1/PD-1-mediated synapse formation between eosinophils and T cells. We also demonstrate that eosinophils suppress T lymphocyte responses through the inhibition of T cell receptor/CD3 (TCR/CD3) subunit association and signal transduction in an inducible NOS-dependent manner. Increasing local eosinophil concentration, through administration of intratracheal eotaxin and IL-5, can ameliorate alloimmune responses in the lung allograft. Thus, our data indicate that eosinophil mobilization may be utilized as a novel means of lung allograft-specific immunosuppression.

Eosinophil-derived IL-13 promotes emphysema

The inflammatory responses in chronic airway diseases leading to emphysema are not fully defined. We hypothesised that lung eosinophilia contributes to airspace enlargement in a mouse model and to emphysema in patients with chronic obstructive pulmonary disease (COPD).A transgenic mouse model of chronic type 2 pulmonary inflammation (I5/hE2) was used to examine eosinophil-dependent mechanisms leading to airspace enlargement. Human sputum samples were collected for translational studies examining eosinophilia and matrix metalloprotease (MMP)-12 levels in patients with chronic airways disease.Airspace enlargement was identified in I5/hE2 mice and was dependent on eosinophils. Examination of I5/hE2 bronchoalveolar lavage identified elevated MMP-12, a mediator of emphysema. We showed, in vitro, that eosinophil-derived interleukin (IL)-13 promoted alveolar macrophage MMP-12 production. Airspace enlargement in I5/hE2 mice was dependent on MMP-12 and eosinophil-derived IL-4/13. Consistent with this, MMP-12 was elevated in patients with sputum eosinophilia and computed tomography evidence of emphysema, and also negatively correlated with forced expiratory volume in 1 s.A mouse model of chronic type 2 pulmonary inflammation exhibited airspace enlargement dependent on MMP-12 and eosinophil-derived IL-4/13. In chronic airways disease patients, lung eosinophilia was associated with elevated MMP-12 levels, which was a predictor of emphysema. These findings suggest an underappreciated mechanism by which eosinophils contribute to the pathologies associated with asthma and COPD.

Intravital imaging allows real-time characterization of tissue resident eosinophils

Eosinophils are core components of the immune system, yet tools are lacking to directly observe eosinophils in action in vivo. To better understand the role of tissue resident eosinophils, we used eosinophil-specific CRE (eoCRE) mice to create GFP and tdTomato reporters. We then employed intravital microscopy to examine the dynamic behaviour of eosinophils in the healthy GI tract, mesentery, liver, lymph node, skin and lung. Given the role of eosinophils in allergic airway diseases, we also examined eosinophils in the lung following ovalbumin sensitization and challenge. We were able to monitor and quantify eosinophilic behaviours including patrolling, crawling, clustering, tissue distribution and interactions with other leukocytes. Thus, these reporter mice allow eosinophils to be examined in real-time in living animals, paving the way to further understanding the roles eosinophils play in both health and disease.

Inducible nitric oxide synthase (iNOS) mediated inhibition of T cell receptor (TCR) signaling is a mechanism for eosinophil dependent amelioration of alloimmunity in lung grafts

Eosinophils play a surprising role in downregulating lung graft-specific alloimmunity, even without immunosuppression. We demonstrate here, a mechanism used by eosinophils to downregulate alloimmune responses.

To study the mechanism of eosinophil dependent downregulation of alloimmune responses, we used a model of diphtheria toxin (DT) dependent ablation of eosinophils in iPHIL, a mouse model expressing DT receptor on the eosinophil-peroxidase gene locus. Fully MHC-mismatched Balb/c (H2Kd) lungs were engrafted to iPHIL (H2Kb) recipients without immunosuppression. We modeled alloreactivity in vitro, with mixed leukocyte cultures, comprising Th1-polarized eosinophils as modulators of T cells from C57BL/6J or Nur77-GFP mice stimulated by either allogeneic dendritic cells or anti-CD3/CD28 agonistic antibodies.

Ablation of eosinophils in non-immunosuppressed lung graft recipients leads to enhanced T cell activation and graft rejection. Similarly, in vitro, we observed a dose and contact dependent downregulation of T cell activation by eosinophils. While contact between eosinophils and T cells is mediated through the upregulation of PD-L1 on both wild-type and iNOS−/− eosinophils after TH-1 polarization, the inhibition of T cell activation is iNOS dependent and is directly linked to the iNOS dependent inhibition of the TCR signaling early gene, Nr4a1, monitored in Nur77-GFP mice.

Thus, following contact with T cells, iNOS-expressing eosinophils downregulate lung graft alloimmunity through a direct effect on TCR engagement early genes, leading to the inhibition of T cell activation. This provides an explanation for the surprising observation of lung-graft specific alloimmune downregulation by eosinophils.

Baseline Gastrointestinal Eosinophilia Is Common in Oral Immunotherapy Subjects With IgE-Mediated Peanut Allergy

Rationale: Oral immunotherapy (OIT) is an emerging treatment for food allergy. While desensitization is achieved in most subjects, many experience gastrointestinal symptoms and few develop eosinophilic gastrointestinal disease. It is unclear whether these subjects have subclinical gastrointestinal eosinophilia (GE) at baseline. We aimed to evaluate the presence of GE in subjects with food allergy before peanut OIT.

Methods: We performed baseline esophagogastroduodenoscopies on 21 adults before undergoing peanut OIT. Subjects completed a detailed gastrointestinal symptom questionnaire. Endoscopic findings were assessed using the Eosinophilic Esophagitis (EoE) Endoscopic Reference Score (EREFS) and biopsies were obtained from the esophagus, gastric antrum, and duodenum. Esophageal biopsies were evaluated using the EoE Histologic Scoring System. Immunohistochemical staining for eosinophil peroxidase (EPX) was also performed. Hematoxylin and eosin and EPX stains of each biopsy were assessed for eosinophil density and EPX/mm² was quantified using automated image analysis.

Results: All subjects were asymptomatic. Pre-existing esophageal eosinophilia (>5 eosinophils per high-power field [eos/hpf]) was present in five participants (24%), three (14%) of whom had >15 eos/hpf associated with mild endoscopic findings (edema, linear furrowing, or rings; median EREFS = 0, IQR 0–0.25). Some subjects also demonstrated basal cell hyperplasia, dilated intercellular spaces, and lamina propria fibrosis. Increased eosinophils were noted in the gastric antrum (>12 eos/hpf) or duodenum (>26 eos/hpf) in 9 subjects (43%). EPX/mm² correlated strongly with eosinophil counts (r = 0.71, p < 0.0001).

Conclusions: Pre-existing GE is common in adults with IgE-mediated peanut allergy. Eosinophilic inflammation (EI) in these subjects may be accompanied by mild endoscopic and histologic findings. Longitudinal data collection during OIT is ongoing.

Revisiting the NIH Taskforce on the Research needs of Eosinophil-Associated Diseases (RE-TREAD)

Eosinophil-associated diseases (EADs) are rare, heterogeneous disorders characterized by the presence of eosinophils in tissues and/or peripheral blood resulting in immunopathology. The heterogeneity of tissue involvement, lack of sufficient animal models, technical challenges in working with eosinophils, and lack of standardized histopathologic approaches have hampered progress in basic research. Additionally, clinical trials and drug development for rare EADs are limited by the lack of primary and surrogate endpoints, biomarkers, and validated patient-reported outcomes. Researchers with expertise in eosinophil biology and eosinophil-related diseases reviewed the state of current eosinophil research, resources, progress, and unmet needs in the field since the 2012 meeting of the NIH Taskforce on the Research of Eosinophil-Associated Diseases (TREAD). RE-TREAD focused on gaps in basic science, translational, and clinical research on eosinophils and eosinophil-related pathogenesis. Improved recapitulation of human eosinophil biology and pathogenesis in murine models was felt to be of importance. Characterization of eosinophil phenotypes, the role of eosinophil subsets in tissues, identification of biomarkers of eosinophil activation and tissue load, and a better understanding of the role of eosinophils in human disease were prioritized. Finally, an unmet need for tools for use in clinical trials was emphasized. Histopathologic scoring, patient- and clinician-reported outcomes, and appropriate coding were deemed of paramount importance for research collaborations, drug development, and approval by regulatory agencies. Further exploration of the eosinophil genome, epigenome, and proteome was also encouraged. Although progress has been made since 2012, unmet needs in eosinophil research remain a priority.

Eosinophils alleviate lung allograft rejection through their modulation of CD8+ T Cells

Introduction

Based on the accumulation of eosinophils (eos) in rejected lung grafts, it was widely held that eos perpetuate lung graft rejection. However, we showed recently in a mechanistic study that eos mediate lung graft tolerance. As eos are also present in rejected lungs, we therefore explore the possibility of a different role of eos in lung graft rejection.

Method

Using orthotopic left lung transplantation of MHC-1 mismatched Balb/c (H2Kd) donors to C57BL/6J (H2Kb) recipients, with or without co-stimulatory blockade immunosuppression, we quantified the number of eos in lung grafts at day 7 post-transplant (D7). Th1, Th2 and Th17 cytokine profiles of D4 lung grafts were analyzed by quantitative PCR. D7 eos were also analyzed for their expression of Th1, Th2 and Th17 signature genes. The role of eos was examined in iPHIL mice that experience selective ablation of eos after Diphtheria toxin (DT) administration. Balb/c left lungs transplanted into DT or vehicle treated iPHIL mice without immunosuppression were analyzed histologically and flow cytometrically at D4.

Results

We observed similar numbers of eos, higher Th1 polarization, lower IL33, a Th2 cytokine and less Th17 polarization of the lung microenvironment, and higher expression of the Th1 signature genes among eos, in rejecting compared to accepting lung grafts. Eos deficiency was associated with more rapid lung graft rejection, evidenced in higher CD8+ T cell proliferation, lower CD4/CD8 ratio, and enhanced T cell differentiation to effector memory phenotype.

Conclusion

Our results indicate that eos directly ameliorate lung graft rejection even in the absence of immunosuppression. This calls for a revalidation of the importance of eos in lung allograft pathology.

Shaping eosinophil identity in the tissue contexts of development, homeostasis, and disease

Eosinophils play homeostatic roles in different tissues and are found in several organs at a homeostatic baseline, though their tissue numbers increase significantly in development and disease. The morphological, phenotypical, and functional plasticity of recruited eosinophils are influenced by the dynamic tissue microenvironment changes between homeostatic, morphogenetic, and disease states. Activity of the epithelial-mesenchymal interface, extracellular matrix, hormonal inputs, metabolic state of the environment, as well as epithelial and mesenchymal-derived innate cytokines and growth factors all have the potential to regulate the attraction, retention, in situ hematopoiesis, phenotype, and function of eosinophils. This review examines the reciprocal relationship between eosinophils and such tissue factors, specifically addressing: (1) tissue microenvironments associated with the presence and activity of eosinophils; (2) non-immune tissue ligands regulatory for eosinophil accumulation, hematopoiesis, phenotype, and function (with an emphasis on the extracellular matrix and epithelial-mesenchymal interface); (3) the contribution of eosinophils to regulating tissue biology; (4) eosinophil phenotypic heterogeneity in different tissue microenvironments, classifying eosinophils as progenitors, steady state eosinophils, and Type 1 and 2 activated phenotypes. An appreciation of eosinophil regulation by non-immune tissue factors is necessary for completing the picture of eosinophil immune activation and understanding the functional contribution of these cells to development, homeostasis, and disease.

Eosinophils promote inducible NOS-mediated lung allograft acceptance

Lungs allografts have worse long-term survival compared with other organ transplants. This is most likely due to their unique immunoregulation that may not respond to traditional immunosuppression. For example, local NO generation by inducible NOS (iNOS) is critical for lung allograft acceptance but associates with rejection of other solid organs. The source of NO in accepting lung allografts remains unknown. Here, we report that, unlike the case for other pulmonary processes in which myeloid cells control NO generation, recipient-derived eosinophils play a critical and nonredundant role in iNOS-mediated lung allograft acceptance. Depletion of eosinophils reduces NO levels to that of recipients with global deletion of iNOS and leads to a costimulatory blockade-resistant form of rejection. Furthermore, NO production by eosinophils depends on Th1 polarization by inflammatory mediators, such as IFN-γ and TNF-α. Neutralization of such mediators abrogates eosinophil suppressive capacity. Our data point to what we believe to be a unique and previously unrecognized role of eosinophil polarization in mediating allograft tolerance and put into perspective the use of high-dose eosinophil-ablating corticosteroids after lung transplantation.

Normalized serum eosinophil peroxidase levels are inversely correlated with esophageal eosinophilia in eosinophilic esophagitis

Eosinophil peroxidase is an eosinophil-specific, cytoplasmic protein stored in the secondary granules of eosinophils. While eosinophil peroxidase deposition is increased in the esophagus in eosinophilic esophagitis (EOE), its potential role as a peripheral marker is unknown. This study aims to examine the relationship between serum eosinophil peroxidase and esophageal eosinophilia in eosinophilic esophagitis. Prospectively collected serum from 19 subjects with incident EoE prior to treatment and 20 non-EoE controls were tested for serum eosinophil peroxidase, eosinophilic cationic protein, and eosinophil derived neurotoxin using ELISA. Matching esophageal tissue sections were stained and assessed for eosinophil peroxidase deposition using a histopathologic scoring algorithm. Mean peripheral blood absolute eosinophil counts in eosinophilic esophagitis subjects were significantly elevated compared to controls (363 vs. 195 cells/μL, P = 0.008). Absolute median serum eosinophil peroxidase, eosinophil cationic protein, and eosinophil derived neurotoxin did not differ between groups; however, when normalized for absolute eosinophil counts, eosinophilic esophagitis subjects had significantly lower median eosinophil peroxidase levels (2.56 vs. 6.96 ng/mL per eos/μL, P = 0.002, AUC 0.79 (0.64, 0.94 95% CI)). Multivariate analysis demonstrated this relationship persisted after controlling for atopy. Esophageal biopsies from eosinophilic esophagitis subjects demonstrated marked eosinophil peroxidase deposition (median score 46 vs. 0, P < 0.0001). Normalized eosinophil peroxidase levels inversely correlated with esophageal eosinophil density (r = -0.41, P = 0.009). In contrast to marked tissue eosinophil degranulation, circulating eosinophils appear to retain their granule proteins in EoE. Investigations of normalized serum eosinophil peroxidase levels as a biomarker of EoE are ongoing.

Sputum autoantibodies in patients with severe eosinophilic asthma

BACKGROUND

The persistence of eosinophils in sputum despite high doses of corticosteroids indicates disease severity in asthmatic patients. Chronic inflamed airways can lose tolerance over time to immunogenic entities released on frequent eosinophil degranulation, which further contributes to disease severity and necessitates an increase in maintenance corticosteroids.

OBJECTIVES

We sought to investigate the possibility of a polyclonal autoimmune event in the airways of asthmatic patients and to identify associated clinical and molecular characteristics.

METHODS

The presence of autoantibodies against eosinophil peroxidase (EPX) and anti-nuclear antibodies was investigated in patients with eosinophilic asthma maintained on high-dose corticosteroids, prednisone, or both. The ability of sputum immunoglobulins to induce eosinophil degranulation in vitro was assessed. In addition, the associated inflammatory microenvironment in patients with detectable autoantibodies was examined.

RESULTS

We report a "polyclonal" autoimmune event occurring in the airways of prednisone-dependent asthmatic patients with increased eosinophil activity, recurrent pulmonary infections, or both, as evident by the concomitant presence of sputum anti-EPX and anti-nuclear antibodies of the IgG subtype. Extensive cytokine profiling of sputum revealed a T_H2-dominated microenvironment (eotaxin-2, IL-5, IL-18, and IL-13) and increased signalling molecules that support the formation of ectopic lymphoid structures (B-cell activating factor and B cell-attracting chemokine 1). Immunoprecipitated sputum immunoglobulins from patients with increased autoantibody levels triggered eosinophil degranulation in vitro, with release of extensive histone-rich extracellular traps, an event unsuppressed by dexamethasone and possibly contributing to the steroid-unresponsive nature of these eosinophilic patients.

CONCLUSION

This study identifies an autoimmune endotype of severe asthma that can be identified by the presence of sputum autoantibodies against EPX and autologous cellular components.

Lung Pathologies in a Chronic Inflammation Mouse Model Are Independent of Eosinophil Degranulation

RATIONALE

The release of eosinophil granule proteins in the lungs of patients with asthma has been dogmatically linked with lung remodeling and airway hyperresponsiveness. However, the demonstrated inability of established mouse models to display the eosinophil degranulation occurring in human subjects has prevented a definitive in vivo test of this hypothesis.

OBJECTIVES

To demonstrate in vivo causative links between induced pulmonary histopathologies/lung dysfunction and eosinophil degranulation.

METHODS

A transgenic mouse model of chronic T-helper cell type 2-driven inflammation overexpressing IL-5 from T cells and human eotaxin 2 in the lung (I5/hE2) was used to test the hypothesis that chronic histopathologies and the development of airway hyperresponsiveness occur as a consequence of extensive eosinophil degranulation in the lung parenchyma.

MEASUREMENT AND MAIN RESULTS

Studies targeting specific inflammatory pathways in I5/hE2 mice surprisingly showed that eosinophil-dependent immunoregulative events and not the release of individual secondary granule proteins are the central contributors to T-helper cell type 2-induced pulmonary remodeling and lung dysfunction. Specifically, our studies highlighted a significant role for eosinophil-dependent IL-13 expression. In contrast, extensive degranulation leading to the release of major basic protein-1 or eosinophil peroxidase was not causatively linked to many of the induced pulmonary histopathologies. However, these studies did define a previously unappreciated link between the release of eosinophil peroxidase (but not major basic protein-1) and observed levels of induced airway mucin.

CONCLUSIONS

These data suggest that improvements observed in patients with asthma responding to therapeutic strategies ablating eosinophils may occur as a consequence of targeting immunoregulatory mechanisms and not by simply eliminating the destructive activities of these purportedly end-stage effector cells.

Frontline Science: Eosinophil-deficient MBP-1 and EPX double-knockout mice link pulmonary remodeling and airway dysfunction with type 2 inflammation

Eosinophils and the release of cationic granule proteins have long been implicated in the development of the type 2-induced pathologies linked with respiratory inflammation. Paradoxically, the ablation of the two genes encoding the most abundant of these granule proteins, major basic protein-1 (MBP-1) and eosinophil peroxidase (EPX), results in a near collapse of eosinophilopoiesis. The specificity of this lineage ablation and the magnitude of the induced eosinopenia provide a unique opportunity to clarify the importance of eosinophils in acute and chronic inflammatory settings, as well as to identify potential mechanism(s) of action linked with pulmonary eosinophils in those settings. Specifically, we examined these issues by assessing the induced immune responses and pathologies occurring in MBP-1^-/-/EPX^-/- mice after 1) ovalbumin sensitization/provocation in an acute allergen-challenge protocol, and 2) crossing MBP-1^-/-/EPX^-/- mice with a double-transgenic model of chronic type 2 inflammation (i.e., I5/hE2). Acute allergen challenge and constitutive cytokine/chemokine expression each induced the accumulation of pulmonary eosinophils in wild-type controls that was abolished in the absence of MBP-1 and EPX (i.e., MBP-1^-/-/EPX^-/- mice). The expression of MBP-1 and EPX was also required for induced lung expression of IL-4/IL-13 in each setting and, in turn, the induced pulmonary remodeling events and lung dysfunction. In summary, MBP-1^-/-/EPX^-/- mice provide yet another definitive example of the immunoregulatory role of pulmonary eosinophils. These results highlight the utility of this unique strain of eosinophil-deficient mice as part of in vivo model studies investigating the roles of eosinophils in health and disease settings.

Single-Layer WEBs: Intrasaccular Flow Disrupters for Aneurysm Treatment—Feasibility Results from a European Study

BACKGROUND AND PURPOSE

The safety and efficiency of the dual-layer Woven EndoBridge (WEB) device has already been published. However, this international multicenter study sought to evaluate the safety of single-layer devices, which are the newest generation of the WEB intrasaccular flow-disrupter family. They have been designed to offer smaller-sized devices with a lower profile to optimize navigability and delivery, which may, in turn, broaden their range of use.

MATERIALS AND METHODS

Data from all consecutive patients treated with a single-layer WEB device, in 10 European centers from June 2013 to May 2014 were included. Clinical presentations, technical details, intra- and perioperative complications, and outcomes at discharge were recorded. Clinical and angiographic data at last follow-up were also analyzed when available.

RESULTS

Ninety patients with 98 WEB-treated aneurysms were included in this study. In 93 cases (95%), WEB placement was possible. Complete occlusion at the end of the procedure was obtained in 26 instances (26%). Additional treatment during the procedure (coiling and/or stent placement) was necessary in 12 cases (12.7%). Procedure-related complications occurred in 13 cases, leading to permanent neurologic deficits in 4 patients (4.4%). Early vascular imaging follow-up data were available for 44 patients (57%), with an average time interval of 3.3 months. Treatment-related morbidity and mortality rates at last follow-up were 2.2% and 1.1%, respectively.

CONCLUSIONS

In this study, the feasibility and safety of the single-layer WEB device was comparable with that of the double-layer. However, further studies are needed to evaluate long-term efficacies.

Re-defining the unique roles for eosinophils in allergic respiratory inflammation

The role of eosinophils in the progression and resolution of allergic respiratory inflammation is poorly defined despite the commonality of their presence and in some cases their use as a biomarker for disease severity and/or symptom control. However, this ambiguity belies the wealth of insights that have recently been gained through the use of eosinophil-deficient/attenuated strains of mice that have demonstrated novel immunoregulatory and remodelling/repair functions for these cells in the lung following allergen provocation. Specifically, studies of eosinophil-deficient mice suggest that eosinophils contribute to events occurring in the lungs following allergen provocation at several key moments: (i) the initiating phase of events leading to Th2-polarized pulmonary inflammation, (ii) the suppression Th1/Th17 pathways in lung-draining lymph nodes, (iii) the recruitment of effector Th2 T cells to the lung, and finally, (iv) mechanisms of inflammatory resolution that re-establish pulmonary homoeostasis. These suggested functions have recently been confirmed and expanded upon using allergen provocation of an inducible eosinophil-deficient strain of mice (iPHIL) that demonstrated an eosinophil-dependent mechanism(s) leading to Th2 dominated immune responses in the presence of eosinophils in contrast to neutrophilic as well as mixed Th1/Th17/Th2 variant phenotypes in the absence of eosinophils. These findings highlighted that eosinophils are not exclusively downstream mediators controlled by T cells, dendritic cells (DC) and/or innate lymphocytic cells (ILC2). Instead, eosinophils appear to be more aptly described as significant contributors in complex interrelated pathways that lead to pulmonary inflammation and subsequently promote resolution and the re-establishment of homoeostatic baseline. In this review, we summarize and put into the context the evolving hypotheses that are now expanding our understanding of the roles eosinophils likely have in the lung following allergen provocation.

Case report: a troublesome ophthalmic artery aneurysm

Objective and Importance When treating large unruptured ophthalmic artery (OA) aneurysms causing progressive blindness, surgical clipping is still the preferred method because aneurysm sac decompression may relieve optic nerve compression. However, endovascular treatment of OA aneurysms has made important progress with the introduction of stents. Although this development is welcomed, it also makes the choice of treatment strategy less straightforward than in the past, with the potential of missteps.

Clinical Presentation A 56-year-old woman presented with a long history of progressive unilateral visual loss and magnetic resonance imaging showing a 20-mm left-sided OA aneurysm.

Intervention Because of her long history of very poor visual acuity, we considered her left eye to be irredeemable and opted for endovascular therapy. The OA aneurysms was treated with stent and coils but continued to grow, threatening the contralateral eye. Because she failed internal carotid artery (ICA) balloon test occlusion, we performed a high-flow extracranial-intracranial bypass with proximal ICA occlusion in the neck. However, aneurysm growth continued due to persistent circulation through reversed blood flow in distal ICA down to the OA and the cavernous portion of the ICA. Due to progressive loss of her right eye vision, we surgically occluded the ICA proximal to the posterior communicating artery and excised the coiled, now giant, OA aneurysm. This improved her right eye vision, but her left eye was permanently blind.

Conclusion This case report illustrates complications of the endovascular and surgical treatment of a large unruptured OA aneurysm.

Eosinophil shape change and secretion

The analysis of eosinophil shape change and mediator secretion is a useful tool in understanding how eosinophils respond to immunological stimuli and chemotactic factors. Eosinophils undergo dramatic shape changes, along with secretion of the granule-derived enzyme eosinophil peroxidase (EPX) in response to chemotactic stimuli including platelet-activating factor and CCL11 (eotaxin-1). Here, we describe the analysis of eosinophil shape change by confocal microscopy analysis and provide an experimental approach for comparing unstimulated cells with those that have been stimulated to undergo chemotaxis. In addition, we illustrate two different degranulation assays for EPX using OPD and an enzyme-linked immunosorbent assay technique and show how eosinophil degranulation may be assessed from in vitro as well as ex vivo stimulation.