Active eosinophils regulate host defence and immune responses in colitis

Inflammation and IL-4 regulate Parkinson's and Crohn's disease associated kinase LRRK2

Mutations in Leucine-Rich Repeat protein Kinase 2 (LRRK2) are associated with Parkinson's disease (PD) and Crohn's disease (CD), but the regulation of LRRK2 during inflammation remains relatively unexplored. Here we describe the development of a flow cytometry-based assay to assess LRRK2 activity in individual cells and the generation of an EGFP-Lrrk2 knock-in reporter mouse to analyse cell-specific LRRK2 expression. Using these tools, we measured LRRK2 levels and activity in murine splenic and intestinal immune cells and in human blood. Anti-CD3 induced inflammation increases LRRK2 expression and activity in B cells and monocytes, while in mature neutrophils, inflammation stimulates activity but reduces LRRK2 expression. A kinase-activating PD-associated LRRK2-R1441C mutation exacerbates inflammation-induced activation of LRRK2 specifically in monocytes and macrophages. We identify IL-4 as a novel T-cell-derived factor that upregulates LRRK2 expression and activity in B cells, replicating inflammatory effects observed in vivo. Our findings provide valuable new insights into the regulation of the LRRK2 pathway in immune cells, crucial for understanding LRRK2 and its therapeutic potential in inflammatory diseases such as CD.

Beta-Sitosterol-Conjugated Sinapic Acid-Engineered Nanoliposome: Biomucoadhesive and Enzyme-Responsive Targeted Oral Therapy in Ulcerative Colitis

Developing oral drug delivery systems is promising for ulcerative colitis (UC). However, the key challenges, including formulation degradation under harsh gastric conditions, poor targeting efficiency, and limited colonic residence, lead to poor therapeutic efficacy that still needs to be tackled. Effective treatment requires a safe, efficacious, enzyme- and pH-responsive, biomucoadhesive oral drug delivery system to overcome these challenges. Therefore, we have developed chitosan-armored 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) nanoliposomes amalgamated with synthesized beta-sitosterol-sinapic acid (Be-S) conjugate, further encapsulated with 3,4-methylenedioxy-β-nitrostyrene (MNS) as NLRP3 inhibitor, termed C@MN@DMBe-S, to overcome the limitation of free MNS and sinapic acid. Formulated by the thin-film hydration method and processed through extrusion, these unilamellar liposomes demonstrated structural stability and mucoadhesive properties due to chitosan coating. This configuration protected the nanoliposomes from the gastric acidic environment and allowed retention in the inflamed colon for 48 h. The enzyme-responsive C@MN@DMBe-S nanoliposome releases sinapic acid at the inflamed colonic site via esterase activity, providing sustained and controlled release of MNS. This synergistic action delivers antioxidant and anti-inflammatory effects while influencing the gut microbiota composition by releasing short-chain fatty acids. Moreover, therapeutic investigations revealed that C@MN@DMBe-S exhibited superior efficacy compared with free MNS when administered orally. The formulation effectively downregulated NF-κB, NLRP3, Caspase-1, and IL-1β expression while upregulating MUC5AC expression, indicating enhanced anti-inflammatory and protective effects and thereby promoting mucosal healing. In addition, C@MN@DMBe-S was found to regulate immune cell expression and effectively downregulate neutrophil infiltration. This armor- and enzyme-responsive strategy elucidates the impact of oral nanomedicines on mitigating UC and is demonstrated as an effective treatment.

Inflammatory and homeostatic roles of eosinophil subpopulations in chronic rhinosinusitis with nasal polyp pathogenesis

Chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP) mainly expresses type-2 endotype, featuring eosinophils as a main player in the inflammatory process. Prolonged eosinophilia in the tissues of asthma and CRSwNP patients has been associated with structural changes, leading to fixed airflow obstruction in asthma and nasal polyposis in CRSwNP. This suggests that eosinophils may belong to different subgroups playing distinct roles in pathogenesis. Recent studies highlight the roles of inflammatory eosinophils (iEOS) in driving inflammation and tissue damage, whereas tissue-resident eosinophils (rEOS) maintain homeostasis and tissue repair in the airway. Therefore, understanding both roles of eosinophil subpopulations is crucial for better CRSwNP management, including enhancing the diagnosis accuracy, predicting recurrence, and optimizing treatment strategies.

Regulation of eosinophil recruitment and heterogeneity during allergic airway inflammation

Eosinophils represent a granulocyte cell type that is strongly associated with type 2 inflammatory conditions. During steady state conditions few eosinophils are found in lung tissue, though they may contribute to homeostasis. In allergic airway inflammation, eosinophils are strongly increased and associated to disease severity. The underlying type 2 immune response tightly regulates eosinophil development, recruitment, survival, and heterogeneity. Inflammatory eosinophils in the lung are unfavourable, as they can cause tissue damage, amplify type 2 immunity and induce bronchial obstruction by expelling granular proteins and cytokines. In this review we provide an overview about mechanisms regulating development of eosinophils in the bone marrow and their extravasation into the lung including recent findings on induction and diversity of eosinophilia in allergic airway inflammation.

Tartaric Acid Exacerbates DSS-Induced Colitis by Promoting Eosinophilic Inflammation via IL-13 and IL-5Rα Upregulation

Eosinophils are granulocytes involved in the effector phase of type 2 T cell immune responses, which are elevated in inflammatory conditions like ulcerative colitis (UC) and other allergic diseases. UC is a chronic inflammatory colon disease, marked by excessive eosinophil infiltration and elevated Th2 cytokines, which contribute to mucosal inflammation and tissue damage. Dietary factors, including certain organic acids, can influence UC progression by modulating gut immune responses. This research is the first to explore the dose-dependent effects of tartaric acid (TA), a naturally occurring organic acid widely used in the food industry, on eosinophil activation and Th2 cytokine response in both normal mice and a dextran sulfate sodium (DSS)-induced colitis model. Normal mice were treated with TA at varying doses (5 µg, 25 µg, and 50 µg/mouse/day), while colitis mice received 50 µg TA. Eosinophil activation markers (CD11b+, SiglecF+, and CCR3+), Th2 cytokines (IL-4, IL-13, and IL-31), and IL-17 were assessed in peripheral blood leukocytes, lymph nodes, and splenocytes using flow cytometry. Additionally, mRNA expression levels of eosinophil-associated chemokines and cytokines in the splenocytes were quantified with real-time qPCR. Our results demonstrate a dose-dependent effect of TA, with the highest dose (50 µg) significantly increasing eosinophil activation markers, Th2 cytokines, IL-17, and mRNA expression of SiglecF, CCL11, and toll-like receptor 4 in normal mice. In colitis mice, treatment with 50 µg TA showed marked increases in IL-13 levels compared to those of untreated colitis mice, reflecting increased eosinophil recruitment to inflamed tissues. Moreover, mRNA expression of IL-5Rα was elevated in normal mice and colitis mice administered with TA. These results suggest that TA enhances eosinophil proliferation, the upregulation of their regulatory molecules, and Th2 immune profiles, potentially worsening the severity of colitis.

Diagnostic and Prognostic Value of Hematological Parameters in Necrotizing Enterocolitis: A Systematic Review

Background/Objectives: Necrotizing enterocolitis (NEC) is a severe, potentially fatal gastrointestinal disease that primarily affects preterm neonates, especially those with very low birth weight (<1500 g). Despite extensive research, its pathophysiology remains unclear, with NEC considered a spectrum of disorders driven by systemic inflammation, microbiota dysregulation, and intestinal hypoxic injury. Diagnosis is challenging due to its subtle presentation and reliance on clinical and radiographic findings, underscoring the urgent need for reliable early biomarkers. Complete blood count (CBC) is one of the most frequently performed laboratory tests in neonatal care, providing valuable insights associated with hematologic alterations associated with NEC. Given its cost-effectiveness, accessibility, and rapid turnaround time, CBC parameters have been increasingly investigated for their diagnostic and prognostic potential in NEC. This systematic review consolidates existing evidence on the diagnostic and prognostic utility of CBC parameters in NEC, examining their association with disease onset, progression, and outcomes. Methods: A systematic review of the literature in PubMed and Scopus databases was conducted, between February 25 and December 2024. Results: Following a PRISMA-compliant search strategy, 77 eligible studies were included, analyzing data from 295,195 neonates, of whom 14,570 had NEC. Among the 77 studies, 17 examined NEC-associated mortality as a primary outcome, while 13 studies focused on the development of predictive models incorporating CBC parameters alongside other clinical and laboratory data to assess NEC severity and prognosis in neonates. The findings highlight the potential of CBC-derived markers to facilitate early NEC detection and risk stratification. However, variations in study design and diagnostic criteria highlight the need for prospective studies to validate their clinical use. Conclusions: Despite advancements in understanding NEC, its diagnosis remains challenging due to the absence of fully reliable biomarkers. CBC parameters show promise in offering early diagnostic and prognostic insights. However, further validation is needed for their routine integration into NICU practice. Given the persistent challenges in NEC diagnosis and management, our findings highlight the necessity for integrated scoring systems that combine hematologic, clinical, and radiologic data to enhance early detection and optimize neonatal care. Further research is essential to refine these predictive models, enabling timely interventions and improving survival rates in NEC-affected neonates.

Eosinophil innate immune memory after bacterial skin infection promotes allergic lung inflammation

Microbial exposure at barrier interfaces drives development and balance of the immune system, but the consequences of local infections for systemic immunity and secondary inflammation are unclear. Here, we show that skin exposure to the bacterium Staphylococcus aureus persistently shapes the immune system of mice with specific impact on progenitor and mature bone marrow neutrophil and eosinophil populations. The infection-imposed changes in eosinophils were long-lasting and associated with functional as well as imprinted epigenetic and metabolic changes. Bacterial exposure enhanced cutaneous allergic sensitization and resulted in exacerbated allergen-induced lung inflammation. Functional bone marrow eosinophil reprogramming and pulmonary allergen responses were driven by the alarmin interleukin-33 and the complement cleavage fragment C5a. Our study highlights the systemic impact of skin inflammation and reveals mechanisms of eosinophil innate immune memory and organ cross-talk that modulate systemic responses to allergens.

Emerging Roles of Eosinophils in Bone

PURPOSE OF THE REVIEW

Eosinophils are traditionally known for their role in immune defense against parasites and their involvement in various immunopathologies, including eosinophilic airway diseases, eosinophilic dermatoses, and gastrointestinal disorders. However, recent findings from our group and other leading laboratories have broadened this perspective, revealing that eosinophils also play crucial roles in tissue development, homeostasis, and regeneration. This review aims to highlight the regulatory functions of eosinophils within the bone niche and emphasize the importance of further research into their role in bone biology.

RECENT FINDINGS

Growing evidence suggests that eosinophils are key regulators of bone metabolism, extending beyond their established roles in immunity and inflammation. They contribute to bone homeostasis by inhibiting osteoclast differentiation, helping to prevent excessive bone resorption in osteoporosis and inflammatory arthritis. Additionally, eosinophils may promote osteoblast-mediated bone formation, modulate the mesenchymal and hematopoietic stem cell niche, and contribute to the bone microenvironment by affecting vascularization and extracellular matrix composition. However, their impact may vary under pathological conditions. Patients with eosinophilic disorders are often at an increased risk of osteoporosis and fragility fractures, though this is largely attributed to disease-related treatments rather than eosinophil activity itself. Despite emerging insights into the role of eosinophils in bone biology, the underlying mechanisms remain incompletely understood. Further research is essential to elucidate how eosinophils influence bone physiology and pathology.

Role and mechanism of IL-33 in bacteria infection related gastric cancer continuum: From inflammation to tumor progression

Gastric cancer, a globally prevalent malignant tumor, is characterized by low early diagnosis rate, high metastasis rate, and poor prognosis, particularly in East Asia, Eastern Europe, and South America. Helicobacter pylori (H. pylori) is recognized as the primary risk factor for gastric cancer. However, the fact that fewer than 3 % of infected individuals develop cancer suggests that other bacteria may also influence gastric carcinogenesis. A diverse community of microorganisms may interact with H. pylori, thereby driving disease progression. Here, the role of the cytokine IL-33, a member of the IL-1 family, is scrutinized. Its production can be induced by H. pylori through the activation of specific signaling pathways, and it contributes to the inflammatory environment by promoting the release of pro-inflammatory cytokines. This article reviews the conflicting evidence regarding IL-33's role in the progression from gastritis to gastric cancer and discusses the potential therapeutic implications of targeting the IL-33/ST2 axis, with various antibodies and inhibitors in development or undergoing clinical trials for inflammatory diseases. However, the role of IL-33 in gastric cancer treatment remains to be fully elucidated, with its effects potentially dependent on the cellular context and stage of cancer progression. In summary, this review provides a comprehensive overview of the intricate relationship between gastric microbiota, IL-33, and gastritis - gastric cancer transition, offering insights into potential therapeutic targets and the development of novel treatment strategies.

Harnessing myeloid cells in cancer

Cancer-associated myeloid cells due to their plasticity play dual roles in both promoting and inhibiting tumor progression. Myeloid cells with immunosuppressive properties play a critical role in anti-cancer immune regulation. Cells of different origin, such as tumor associated macrophages (TAMs), tumor associated neutrophils (TANs), myeloid derived suppressor cells (also called MDSCs) and eosinophils are often expanded in cancer patients and significantly influence their survival, but also the outcome of anti-cancer therapies. For this reason, the variety of preclinical and clinical studies to modulate the activity of these cells have been conducted, however without successful outcome to date. In this review, pro-tumor activity of myeloid cells, myeloid cell-specific therapeutic targets, in vivo studies on myeloid cell re-polarization and the impact of myeloid cells on immunotherapies/genetic engineering are addressed. This paper also summarizes ongoing clinical trials and the concept of chimeric antigen receptor macrophage (CAR-M) therapies, and suggests future research perspectives, offering new opportunities in the development of novel clinical treatment strategies.

The Gut Microbiota-Xanthurenic Acid-Aromatic Hydrocarbon Receptor Axis Mediates the Anticolitic Effects of Trilobatin

Current treatments for ulcerative colitis (UC) remain limited, highlighting the need for novel therapeutic strategies. Trilobatin (TLB), a naturally derived food additive, exhibits potential anti-inflammatory properties. In this study, a dextran sulfate sodium (DSS)-induced animal model is used to investigate the effects of TLB on UC. It is found TLB significantly alleviates DSS-induced UC in mice, as evidenced by a reduction in the disease activity index, an increase in colon length, improvement in histopathological lesions. Furthermore, TLB treatment results in a decrease in proinflammatory cytokines and an increase in anti-inflammatory cytokines. TLB mitigates UC by modulating the intestinal microbiota, particularly Akkermansia, which enhances tryptophan metabolism and upregulates the production of xanthurenic acid (XANA). To confirm the role of TLB-induced microbiota changes, experiments are performed with pseudogerm-free mice and fecal transplantation. It is also identified XANA as a key metabolite that mediates TLB's protective effects. Both TLB and XANA markedly activate the aromatic hydrocarbon receptor (AhR). Administration of an AhR antagonist abrogates their protective effects, thereby confirming the involvement of AhR in the underlying mechanism. In conclusion, the study reveals a novel mechanism through which TLB alleviates UC by correcting microbiota imbalances, regulating tryptophan metabolism, enhancing XANA production, and activating AhR.

Type 2 immunity in allergic diseases

Significant advancements have been made in understanding the cellular and molecular mechanisms of type 2 immunity in allergic diseases such as asthma, allergic rhinitis, chronic rhinosinusitis, eosinophilic esophagitis (EoE), food and drug allergies, and atopic dermatitis (AD). Type 2 immunity has evolved to protect against parasitic diseases and toxins, plays a role in the expulsion of parasites and larvae from inner tissues to the lumen and outside the body, maintains microbe-rich skin and mucosal epithelial barriers and counterbalances the type 1 immune response and its destructive effects. During the development of a type 2 immune response, an innate immune response initiates starting from epithelial cells and innate lymphoid cells (ILCs), including dendritic cells and macrophages, and translates to adaptive T and B-cell immunity, particularly IgE antibody production. Eosinophils, mast cells and basophils have effects on effector functions. Cytokines from ILC2s and CD4+ helper type 2 (Th2) cells, CD8 + T cells, and NK-T cells, along with myeloid cells, including IL-4, IL-5, IL-9, and IL-13, initiate and sustain allergic inflammation via T cell cells, eosinophils, and ILC2s; promote IgE class switching; and open the epithelial barrier. Epithelial cell activation, alarmin release and barrier dysfunction are key in the development of not only allergic diseases but also many other systemic diseases. Recent biologics targeting the pathways and effector functions of IL4/IL13, IL-5, and IgE have shown promising results for almost all ages, although some patients with severe allergic diseases do not respond to these therapies, highlighting the unmet need for a more detailed and personalized approach.

The C-type lectin receptor MINCLE interferes with eosinophil function and protective intestinal immunity in Strongyloides ratti-infected mice

Strongyloides ratti is a helminth parasite that displays tissue-migrating and intestinal life stages. Myeloid C-type lectin receptors (CLRs) are pattern recognition receptors that recognize pathogen-derived ligands and initiate immune responses. To date, the role of CLRs in S. ratti infection has not been investigated. Here, we show that S. ratti-derived ligands are recognized by the CLR Macrophage inducible Ca2+-dependent lectin receptor (MINCLE). While MINCLE-deficiency did not affect initiation of a protective anti-S. ratti type 2 immunity, MINCLE-deficient mice had a transient advantage in intestinal immunity. Unravelling the underlying mechanism, we show that next to macrophages, dendritic cells and neutrophils, a fraction of eosinophils express MINCLE and expand during S. ratti infection. MINCLE-deficient eosinophils exhibited a more active phenotype and prolonged expansion in vivo and displayed increased capacity to reduce S. ratti motility and produce reactive oxygen species in vitro, compared to wild-type (WT) eosinophils. Depletion of eosinophils in S. ratti-infected mice after the tissue-migration phase elevated intestinal worm burden in MINCLE-deficient mice to the WT level. Thus, our findings establish a central contribution of eosinophils to parasite ejection from the intestine and suggest that S. ratti-triggered signalling via MINCLE interferes with eosinophil mediated ejection of S. ratti from the intestine.

Eosinophil Depletion as a Potential Therapeutic Strategy in Acute and Chronic Intestinal Inflammation Based on a Dextran Sulfate Sodium Colitis Model

BACKGROUND

A role for eosinophils in intestinal inflammation and fibrosis in the context of inflammatory bowel disease has been suggested, yet the precise nature, whether causal or secondary remains debated. Hence, it remains unclear whether targeting eosinophils should be further explored as a treatment option in inflammatory bowel disease.

METHODS

Acute and chronic dextran sulfate sodium colitis was induced in wild-type C57BL/6 mice. Eosinophils were depleted by anti-CCR3 injections before colitis induction in a chronic model and after colitis onset in an acute model in order to investigate the impact of eosinophil depletion on pre-existing colitis. Inflammation was assessed using the disease activity index, macroscopic damage, and histological disease activity score. In the chronic model, fibrosis was assessed by examining colon weight/length ratio, collagen deposition through Martius Scarlet Blue staining, hydroxyproline assay, and COL1A1 expression. Protein and gene expression were assessed using the Meso Scale Discovery platform and real-time quantitative polymerase chain reaction.

RESULTS

In the acute and chronic colitis model, eosinophil depletion resulted in reduced disease activity and faster recovery, as observed via the total area under the curve of the disease activity index (P = .004 and P = .02, respectively), macroscopic damage score (P = .009 and P = .08, respectively), and histological disease activity score (P = .09 and P = .002, respectively). In the acute model, the accelerated recovery was accompanied by an increase in interleukin (IL)-10 (P = .03) and a decrease in IL-4 (P = .03) and IL-6 (P = .009). Colon weight/length ratio and collagen deposition were not affected by eosinophil depletion.

CONCLUSIONS

Eosinophil depletion prevents and decreases intestinal inflammation in a preclinical dextran sulfate sodium model without affecting fibrosis. These results pave the way for exploring eosinophil depletion as a novel treatment modality in addressing intestinal inflammation.

Eosinophils Enhance Granuloma-Mediated Control of Persistent Salmonella Infection

Salmonella enterica can persist asymptomatically within tissues for extended periods. This remarkable feat is achieved through intricate host-pathogen interactions in immune cell aggregates called granulomas, wherein Salmonella find favorable cellular niches to exploit while the host limits its expansion and tissue dissemination. Here, using a mouse model of persistent Salmonella infection, we identify a host-protective role of eosinophils in control of Salmonella Typhimurium (STm) infection within the mesenteric lymph nodes (MLN), the main lymphoid tissue of STm persistence. Combining spatial transcriptomics and experimental manipulations, we found that macrophages responding to STm infection recruited eosinophils in a C-C motif chemokine ligand 11 (CCL11)-dependent manner and enhanced their activation. Eosinophil deficiencies increased Salmonella burdens, which was associated with altered granuloma size and impaired type-1 immunity in the MLN. Thus, eosinophils play a vital role in restraining Salmonella exploitation of granuloma macrophages at a key site of bacterial persistence.

The TGF-β mimic TGM4 achieves cell specificity through combinatorial surface co-receptor binding

The immunoregulatory cytokine TGF-β is pleiotropic due to the near-ubiquitous expression of the TGF-β receptors TβRI and TβRII on diverse cell types. The helminth parasite Heligmosomoides polygyrus has convergently evolved a family of TGF-β mimics (TGMs) that bind both these receptors through domains 1-3 of a 5-domain protein. One member of this family, TGM4, differs from TGF-β in acting in a cell-specific manner, failing to stimulate fibroblasts, but activating SMAD phosphorylation in macrophages. Primarily through domains 4 and 5, TGM4 interacts with multiple co-receptors, including CD44, CD49d (integrin α4) and CD206, and can up- and downmodulate macrophage responses to IL-4 and lipopolysaccharide (LPS), respectively. The dependence of TGM4 on combinatorial interactions with co-receptors is due to a moderated affinity for TβRII that is more than 100-fold lower than for TGF-β. Thus the parasite has elaborated TGF-β receptor interactions to establish cell specificity through combinatorial cis-signalling, an innovation absent from the mammalian cytokine.

Leveraging thiol-functionalized biomucoadhesive hybrid nanoliposome for local therapy of ulcerative colitis

Directly administering medication to inflamed intestinal sites for treating ulcerative colitis (UC), poses significant challenges like retention time, absorption variability, side effects, drug stability, and non-specific delivery. Recent advancements in therapy to treat colitis aim to improve local drug availability that is enema therapy at the site of inflammation, thereby reducing systemic adverse effects. Nevertheless, a key limitation lies in enemas' inability to sustain medication in the colon due to rapid peristaltic movement, diarrhea, and poor local adherence. Therefore, in this work, we have developed site-specific thiolated mucoadhesive anionic nanoliposomes to overcome the limitations of conventional enema therapy. The thiolated delivery system allows prolonged residence of the delivery system at the inflamed site in the colon, confirmed by the adhesion potential of thiolated nanoliposomes using in-vitro and in-vivo models. To further provide therapeutic efficacy thiolated nanoliposomes were loaded with gallic acid (GA), a natural compound known for its antibacterial, antioxidant, and potent anti-inflammatory properties. Consequently, Gallic Acid-loaded Thiolated 2,6 DALP DMPG (GATh@APDL) demonstrates the potential for targeted adhesion to the inflamed colon, facilitated by their small size 100 nm and anionic nature. Therapeutic studies indicate that this formulation offers protective effects by mitigating colonic inflammation, downregulating the expression of NF-κB, HIF-1α, and MMP-9, and demonstrating superior efficacy compared to the free GA enema. The encapsulated GA inhibits the NF-κB expression, leading to enhanced expression of MUC2 protein, thereby promoting mucosal healing in the colon. Furthermore, GATh@APDL effectively reduces neutrophil infiltration and regulates immune cell quantification in colonic lamina propria. Our findings suggest that GATh@APDL holds promise for alleviating UC and addressing the limitations of conventional enema therapy.

Challenges and Opportunities in the Clinical Translation of High-Resolution Spatial Transcriptomics

Pathology has always been fueled by technological advances. Histology powered the study of tissue architecture at single-cell resolution and remains a cornerstone of clinical pathology today. In the last decade, next-generation sequencing has become informative for the targeted treatment of many diseases, demonstrating the importance of genome-scale molecular information for personalized medicine. Today, revolutionary developments in spatial transcriptomics technologies digitalize gene expression at subcellular resolution in intact tissue sections, enabling the computational analysis of cell types, cellular phenotypes, and cell-cell communication in routinely collected and archival clinical samples. Here we review how such molecular microscopes work, highlight their potential to identify disease mechanisms and guide personalized therapies, and provide guidance for clinical study design. Finally, we discuss remaining challenges to the swift translation of high-resolution spatial transcriptomics technologies and how integration of multimodal readouts and deep learning approaches is bringing us closer to a holistic understanding of tissue biology and pathology.

Interleukin-33 induces angiogenesis after myocardial infarction via AKT/eNOS signaling pathway

Myocardial infarction (MI) is one of the leading causes of mortality and morbidity worldwide. MI-damaged vascular structures are difficult to completely restore due to the heart's low regenerative capacity. Given interleukin-33 (IL-33) as a potent endothelial activator promoting angiogenesis, this study investigated the role of IL-33 in angiogenesis and cardiac repair after MI. A mouse model of MI was established. IL-33 improved cardiac function and induced an increase in vascular density after MI. Besides, IL-33 promoted human endothelial cells proliferation, migration, and differentiation under both normoxic and hypoxic conditions, consistently with increased angiogenesis in vivo. Mechanistic studies demonstrated that IL-33 could promote angiogenesis by activating eNOS and AKT, and stimulating NO production in vivo and in vitro. Given that injection of exogenous IL-33 induced an inflammatory response, we employed a multifunctional biomimetic nanoparticle drug delivery system to deliver IL-33, thereby enhancing its targeting to the heart for fibrotic therapy and reducing inflammation. In conclusion, our results indicate that IL-33 promotes endothelial angiogenesis after MI through AKT/eNOS/NO signaling pathway. PM&EM/IL-33 nanoparticles may hold promising therapeutic potential for protecting cardiac ischemic injury and mitigating inflammation.

Synovial regulatory T cells expressing ST2 deteriorate joint inflammation through the suppression of immunoregulatory eosinophils

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic polyarthritis. It is well-established that helper T cells play crucial roles in the development and deterioration of RA. Recent studies also revealed the significant roles of regulatory T (Treg) cells in this context. Although Treg cells distributed in peripheral tissues exhibit various functions, the characteristics of synovial Treg cells remain unknown. In this study, we demonstrate that synovial Treg cells exacerbate synovial inflammation by reducing the number of immunoregulatory eosinophils through competitive consumption of IL-33. Synovial Treg cells expressed ST2 in a murine arthritis model, and surprisingly, Treg-specific ST2 knockout (ST2ΔTreg) mice exhibited attenuated arthritis. In ST2ΔTreg mice, an increase in immunoregulatory synovial eosinophils was observed. Additionally, immunoregulatory eosinophils were found to express ST2, and ST2-expressing Treg cells controlled the abundance of immunoregulatory eosinophils, possibly by consuming IL-33. Our results highlight that a subset of synovial Treg cells possesses the machinery to worsen arthritis by suppressing eosinophils. In the future landscape where Treg cell-based therapies are employed for autoimmune diseases, it is important to comprehend the characteristics of disease-related Treg cells. Understanding these aspects is crucial for ensuring safer treatment modalities that do not inadvertently worsen the diseases.

Spatially restricted immune and microbiota-driven adaptation of the gut

The intestine is characterized by an environment in which host requirements for nutrient and water absorption are consequently paired with the requirements to establish tolerance to the outside environment. To better understand how the intestine functions in health and disease, large efforts have been made to characterize the identity and composition of cells from different intestinal regions1-8. However, the robustness, nature of adaptability and extent of resilience of the transcriptional landscape and cellular underpinning of the intestine in space are still poorly understood. Here we generated an integrated resource of the spatial and cellular landscape of the murine intestine in the steady and perturbed states. Leveraging these data, we demonstrated that the spatial landscape of the intestine was robust to the influence of the microbiota and was adaptable in a spatially restricted manner. Deploying a model of spatiotemporal acute inflammation, we demonstrated that both robust and adaptable features of the landscape were resilient. Moreover, highlighting the physiological relevance and value of our dataset, we identified a region of the middle colon characterized by an immune-driven multicellular spatial adaptation of structural cells to the microbiota. Our results demonstrate that intestinal regionalization is characterized by robust and resilient structural cell states and that the intestine can adapt to environmental stress in a spatially controlled manner through the crosstalk between immunity and structural cell homeostasis.

Spatial adaptation of eosinophils and their emerging roles in homeostasis, infection and disease

Eosinophils are bone marrow-derived granulocytes that are traditionally associated with type 2 immune responses, such as those that occur during parasite infections and allergy. Emerging evidence demonstrates the remarkable functional plasticity of this elusive cell type and its pleiotropic functions in diverse settings. Eosinophils broadly contribute to tissue homeostasis, host defence and immune regulation, predominantly at mucosal sites. The scope of their activities primarily reflects the breadth of their portfolio of secreted mediators, which range from cytotoxic cationic proteins and reactive oxygen species to multiple cytokines, chemokines and lipid mediators. Here, we comprehensively review basic eosinophil biology that is directly related to their activities in homeostasis, protective immunity, regeneration and cancer. We examine how dysregulation of these functions contributes to the physiopathology of a broad range of inflammatory diseases. Furthermore, we discuss recent findings regarding the tissue compartmentalization and adaptation of eosinophils, shedding light on the factors that likely drive their functional diversification within tissues.

Granzyme K+CD8+ T cells interact with fibroblasts to promote neutrophilic inflammation in nasal polyps

Sophisticated interactions between stromal and immune cells play crucial roles in various biological and pathological processes. In chronic rhinosinusitis with nasal polyps (CRSwNP), the upper airway inflammation in many patients is driven by TH2, ILC2, and eosinophils, thus being treated with glucocorticoids and anti-type 2 inflammation biologics. The resistance to these therapies is often associated with neutrophilic inflammation, which has also been widely identified in CRSwNP, but the underlying mechanisms remain unclear. Using single-cell analysis, spatial transcriptomics, and T-cell receptor sequencing, we identify an increased presence of granzyme K+(GZMK+) CD8+ T cells in NPs, which possess a phenotype distinct from the cytotoxic GZMB+ effector CD8+ T subset. GZMK+CD8+ T cells are found to express CXCR4 and interact with CXCL12-secreting fibroblasts, inducing the latter to produce neutrophil chemoattractants in a manner uniquely mediated by GZMK but not other granzymes. This GZMK+CD8+ T cell-fibroblast crosstalk is also observed in other inflammatory diseases. Furthermore, GZMK+CD8+ T cells exhibit a selective expansion of clones that recognize Epstein-Barr virus. Here, we show that GZMK marks a phenotypically distinct subset of effector CD8+ T cells that promote neutrophilic inflammation.

Advancing toward a unified eosinophil signature from transcriptional profiling

Eosinophils are granulocytes that can accumulate in increased numbers in tissues and/or peripheral blood in disease. Phenotyping of eosinophils in health and disease has the potential to improve the precision of diagnosis and choice of therapies for eosinophilic-associated diseases. Transcriptional profiling of eosinophils has been plagued by cell fragility and difficulty isolating high-quality RNA. With several technological advances, single-cell RNA sequencing has become possible with eosinophils, at least from mice, while bulk RNA sequencing and microarrays have been performed in both murine and human samples. Anticipating more eosinophil transcriptional profiles in the coming years, we provide a summary of prior studies conducted on mouse and human eosinophils in blood and tissue, with a discussion of the advantages and potential pitfalls of various approaches. Common technical standards in studying eosinophil biology would help advance the field and make cross-study comparisons possible. Knowledge gaps and opportunities include identifying a minimal set of genes that define the eosinophil lineage, comparative studies between active disease and remission vs. homeostasis or development, especially in humans, and a comprehensive comparison between murine and human eosinophils at the transcriptional level. Characterizing such transcriptional patterns will be important to understanding the complex and diverse roles of eosinophils in both health and disease.

Eosinophils as modulators of host defense during parasitic, fungal, bacterial, and viral infections

Eosinophils, traditionally associated as central innate effector cells with type 2 immunity during allergic and helminth parasitic diseases, have recently been revealed to have important roles in tissue homeostasis as well as host defense in a broader variety of infectious diseases. In a dedicated session at the 2023 biennial conference of the International Eosinophil Society titled "Eosinophils in Host Defense," the multifaceted roles eosinophils play against diverse pathogens, ranging from parasites to fungi, bacteria, and viruses, were presented. In this review, the session speakers offer a comprehensive summary of recent discoveries across pathogen classes, positioning eosinophils as pivotal leukocytes in both host defense and pathology. By unraveling the intricacies of eosinophil engagement in host resistance, this exploration may provide valuable insights not only to understand specific underpinnings of eosinophil functions related to each class of pathogens but also to develop novel therapeutics effective against a broad spectrum of infectious diseases.

Eosinophils respond to, but are not essential for control of an acute Salmonella enterica serovar Typhimurium infection in mice

Eosinophils are a highly abundant cell type in the gastrointestinal tract during homeostatic conditions, where they have recently been reported to take on an activated phenotype following colonization by the bacterial microbiota. To date, there have been few studies investigating whether eosinophils respond to infection with enteric bacterial pathogens and/or investigating the requirements for eosinophils for effective bacterial pathogen control. In this study, we investigated the response of eosinophils to an acute enteric infection of mice with the bacterial pathogen Salmonella enterica serovar Typhimurium. We also assessed whether eosinophil deficiency impacted Salmonella burdens in the intestinal tract or impacted the systemic dissemination of Salmonella following an oral infection of littermate wild-type BALB/cJ and eosinophil-deficient ΔdblGATA BALB/cJ mice. We found comparable Salmonella burdens in the intestinal tract of wild-type and eosinophil-deficient mice and no significant differences in the levels of Salmonella disseminating to systemic organs within 3 days of infection. Despite our evidence suggesting that eosinophils are not an essential cell type for controlling bacterial burdens in this acute infection setting, we found higher levels of eosinophils in gut-draining lymph nodes following infection, indicating that eosinophils do respond to Salmonella infection. Our data contribute to the growing evidence that eosinophils are responsive to bacterial stimuli, yet the influence of and requirements for eosinophils during bacterial infection appear to be highly context-dependent.

Phenotypic Shift of an Inflammatory Eosinophil Subset into a Steady-State Resident Phenotype after 2 Years of Vaccination against IL-5 in Equine Insect Bite Hypersensitivity

Eosinophils play a key role in allergic diseases such as insect bite hypersensitivity (IBH). Together with Th2 cells, they shape the course of inflammation in associated type I/IVb allergies. Therefore, a virus-like particle (VLP)-based vaccine targeting equine interleukin-5 (eIL-5), eIL-5-CuMV-TT, was developed to interfere with the IL-5 dependency of eosinophils by inducing the production of anti-self-IL-5 antibodies and alleviating clinical signs in IBH-affected horses. A previous study highlighted the presence of two eosinophil subsets, steady-state resident eosinophils (rEos) and inflammatory eosinophils (iEos), circulating in the blood of healthy and IBH-affected horses, distinguishable by the expression of integrin CD49f. Furthermore, eIL-5-CuMV-TT 1st year vaccination showed a significant decrease of total eosinophils and, in particular, iEos. Nevertheless, the very few remaining eosinophils still shared an iEos phenotype, reflected by bigger size and higher granularity. The aim of this study was to follow up on the phenotype of eosinophils in the 2nd year of vaccination of IBH-affected horses with eIL-5-CuMV-TT. Using flow cytometry analysis of the blood of healthy, IBH, IBH-placebo, and IBH-vaccinated horses, the percentage and count of cells were compared between groups with a focus on pair analysis of eosinophils in 1st and 2nd year vaccinated horses. Our data showed comparably low levels of iEos and a significant increase of rEos in 2nd year compared to 1st year vaccinated horses, suggesting a phenotypic shift toward a resident-like eosinophil population, primarily associated with the phenotype of healthy horses. The reduction of size, granularity, and expression of integrin CD49f in the 2nd year suggests a benefit of long-term treatment with the eIL-5-CuMV-TT vaccine.

Single-cell RNA-sequencing of human eosinophils in allergic inflammation in the esophagus

BACKGROUND

Eosinophils are elusive cells involved in allergic inflammation. Single-cell RNA-sequencing (scRNA-seq) is an emerging approach to deeply characterize cellular properties, heterogeneity, and functionality.

OBJECTIVES

We sought to comprehensively characterize the transcriptome and biological functions of human eosinophils at a site of severe allergic inflammation in the esophagus (ie, eosinophilic esophagitis [EoE]).

METHODS

We employed a gravity-based scRNA-seq methodology to sequence blood eosinophils from patients with EoE and control individuals compared to a reanalyzed public scRNA-seq dataset of human esophageal eosinophils of EoE patients. We used flow cytometry, immunostaining, and a stimulation assay to verify mRNA findings.

RESULTS

In total, scRNA-seq was obtained from 586 eosinophils (188 from blood [n = 6 individuals] and 398 from esophagus [n = 6 individuals]). The esophageal eosinophils were composed of a population of activated eosinophils (enriched in 659 genes compared with peripheral blood-associated eosinophils) and a small population of eosinophils resembling peripheral blood eosinophils (enriched in 62 genes compared with esophageal eosinophils). Esophageal eosinophils expressed genes involved in sensing and responding to diverse stimuli, most notably IFN-γ, IL-10, histamine and leukotrienes, and succinate. Esophageal eosinophils were most distinguished from other esophageal populations by gene expression of the receptors CCR3, HRH4, SUCNR1, and VSTM1; transcription factors CEBPE, OLIG1, and OLIG2; protease PRSS33; and the hallmark eosinophil gene CLC. A web of bidirectional eosinophil interactions with other esophageal populations was derived. Comparing esophageal eosinophils and mast cells revealed that esophageal eosinophils expressed genes involved in DNAX-activation protein-12 (also known as TYROBP) interactions, IgG receptor-triggered events, immunoregulation, and IL-10 signaling.

CONCLUSIONS

In EoE, esophageal eosinophils exist as 2 populations, a minority population resembling blood eosinophils and the other population characterized by high de novo transcription of diverse sensing receptors and inflammatory mediators readying them to potentially intersect with diverse cell types.

Novel insights into the heterogeneity of FOXP3 + Treg cells in drug-induced allergic reactions through single-cell transcriptomics

This study uncovers the novel heterogeneity of FOXP3 + regulatory T (Treg) cells and their pivotal role in modulating immune responses during drug-induced allergic reactions, employing cutting-edge single-cell transcriptomics. We established a mouse model for drug-induced allergic reactions and utilized single-cell RNA sequencing (scRNA-seq) to analyze the transcriptomic landscapes of FOXP3 + Treg cells isolated from affected tissues. The study involved both in vitro and in vivo approaches to evaluate the impact of FOXP3 expression levels on the immunoregulatory functions of Treg cells during allergic responses. Techniques included flow cytometry, cluster analysis, principal component analysis (PCA), CCK8 and CSFE assays for cell proliferation, LDH release assays for toxicity, ELISA for cytokine profiling, and CRISPR/Cas9 technology for gene editing. Our findings revealed significant transcriptomic heterogeneity among FOXP3 + Treg cells in the context of drug-induced allergic reactions, with distinct subpopulations exhibiting unique gene expression profiles. This heterogeneity suggests specialized roles in immune regulation. We observed a decrease in the proliferative capacity and cytokine secretion of FOXP3 + Treg cells following allergic stimulation, alongside an increase in reaction toxicity. Manipulating FOXP3 expression levels directly influenced these outcomes, where FOXP3 deletion exacerbated allergic responses, whereas its overexpression mitigated them. Notably, in vivo experiments demonstrated that FOXP3 overexpression significantly reduced the severity of allergic skin reactions in mice. Our study presents novel insights into the heterogeneity and crucial immunoregulatory role of FOXP3 + Treg cells during drug-induced allergic reactions. Overexpression of FOXP3 emerges as a potential therapeutic strategy to alleviate such allergic responses. These findings contribute significantly to our understanding of immune regulation and the development of targeted treatments for drug-induced allergies.

Activated eosinophils in early life impair lung development and promote long-term lung damage

Exaggeration of type 2 immune responses promotes lung inflammation and altered lung development; however, eosinophils, despite expansion in the postnatal lung, have not been specifically assessed in the context of neonatal lung disease. Furthermore, early life factors including prematurity and respiratory infection predispose infants to chronic obstructive pulmonary disease later in life. To assess eosinophils in the developing lung and how they may contribute to chronic lung disease, we generated mice harboring eosinophil-specific deletion of the negative regulatory enzyme SH2 domain-containing inositol 5' phosphatase-1. This increased the activity and number of pulmonary eosinophils in the developing lung, which was associated with impaired lung development, expansion of activated alveolar macrophages (AMφ), multinucleated giant cell formation, enlargement of airspaces, and fibrosis. Despite regression of eosinophils following completion of lung development, AMφ-dominated inflammation persisted, alongside lung damage. Bone marrow chimera studies showed that SH2 domain-containing inositol 5' phosphatase-1-deficient eosinophils were not sufficient to drive inflammatory lung disease in adult steady-state mice but once inflammation and damage were present, it could not be resolved. Depletion of eosinophils during alveolarization alleviated pulmonary inflammation and lung pathology, demonstrating an eosinophil-intrinsic effect. These results show that the presence of activated eosinophils during alveolarization aggravates AMφs and promotes sustained inflammation and long-lasting lung pathology.

Therapeutic relevance of eosinophilic inflammation and airway viral interactions in severe asthma

The role of eosinophils in airway inflammation and asthma pathogenesis is well established, with raised eosinophil counts in blood and sputum associated with increased disease severity and risk of asthma exacerbation. Conversely, there is also preliminary evidence suggesting antiviral properties of eosinophils in the airways. These dual roles for eosinophils are particularly pertinent as respiratory virus infections contribute to asthma exacerbations. Biologic therapies targeting key molecules implicated in eosinophil-associated pathologies have been approved in patients with severe asthma and, therefore, the effects of depleting eosinophils in a clinical setting are of considerable interest. This review discusses the pathological and antiviral roles of eosinophils in asthma and exacerbations. We also highlight the significant reduction in asthma exacerbations seen with biologic therapies, even at the height of the respiratory virus season. Furthermore, we discuss the implications of these findings in relation to the role of eosinophils in inflammation and antiviral responses to respiratory virus infection in asthma.

Unveiling multifaceted roles of myeloid innate immune cells in the pathogenesis of psoriasis

Psoriasis is a chronic inflammatory skin disease occurring worldwide. Initially viewed as a keratinocyte disorder, psoriasis is now recognized to involve a complex interplay between genetic predisposition, environmental triggers, and a dysregulated immune system, with a significant role of CD4+ T cells producing IL-17. Recent genetic studies have identified susceptibility loci that underscore the importance of innate immune responses, particularly the roles of myeloid cells, such as dendritic cells, macrophages, and neutrophils. These cells initiate and sustain inflammation through cytokine production triggered by external stimuli. They influence keratinocyte behavior and interact with adaptive immune cells. Recent techniques have further revealed the heterogeneity of myeloid cells in psoriatic lesions, highlighting the contributions of less-studied subsets, such as eosinophils and mast cells. This review examines the multifaceted roles of myeloid innate immune cells in psoriasis, emphasizing their functional diversity in promoting psoriatic inflammation. It also describes current treatment targeting myeloid innate immune cells and explores potential new therapeutic strategies based on the functional characteristics of these subsets. Future research should focus on the detailed characterization of myeloid subsets and their interactions to develop targeted treatments that address the complex immune landscape of psoriasis.

The immunoregulatory potential of eosinophil subsets

Eosinophils have traditionally been viewed as pathological effector cells primarily involved in antiparasitic and allergic immune reactions; however, it is becoming increasingly apparent that eosinophils are multifaceted leukocytes that contribute to a variety of roles in both health and disease. Recent research shows that eosinophils play important immunoregulatory roles across various tissue sites including the gastrointestinal tract, adipose tissue, lung, liver, heart, muscles, thymus and bone marrow. With recent advances in our knowledge and appreciation of eosinophil immunoregulatory functions at these tissue sites, as well as emerging research demonstrating the existence of distinct subsets of eosinophils, a review of this topic is timely. Although some questions remain regarding eosinophil function and heterogeneity, this review summarizes the contemporary understanding of the immunoregulatory roles of eosinophils across various tissues and discusses the latest research on eosinophil heterogeneity and subsets.

Single cell RNA sequencing of human eosinophils from nasal polyps reveals eosinophil heterogeneity in chronic rhinosinusitis tissue

BACKGROUND

Chronic rhinosinusitis with nasal polyps (CRSwNP) is characterized by type 2 inflammation in the United States, but the actual roles that eosinophils play in CRSwNP remain largely unclear.

OBJECTIVE

To reveal the roles and heterogeneity of eosinophils in nasal polyp (NP) tissue, we performed single cell RNA sequencing (scRNA-Seq) analysis of NP tissue.

METHODS

Sinonasal tissues (NP and control sinus tissue) and patient matched peripheral blood (PB) samples were obtained from 5 control patients and 5 patients with CRSwNP. Eosinophils were enriched before processing for scRNA-Seq. The gene expression profiles in eosinophils were determined by microwell-based scRNA-Seq technology (BD Rhapsody platform). We predicted the overall function of NP eosinophils by Gene Ontology (geneontology.org) enrichment and pathway analyses and confirmed expression of selected genes by flow cytometry.

RESULTS

After filtering out contaminating cells, we detected 5,542 eosinophils from control PB, 3,883 eosinophils from CRSwNP PB, 101 eosinophils from control sinus tissues (not included in further analyses), and 9,727 eosinophils from NPs by scRNA-Seq. We found that 204 genes were downregulated and 354 genes upregulated in NP eosinophils compared to all PB eosinophils (>1.5-fold, Padj < .05). Upregulated genes in NP eosinophils were associated with activation, cytokine-mediated signaling, growth factor activity, NF-κB signaling, and antiapoptotic molecules. NP eosinophils displayed 4 clusters revealing potential heterogeneity of eosinophils in NP tissue.

CONCLUSIONS

Elevated eosinophils in NP tissue appear to exist in several subtypes that may play important pathogenic roles in CRSwNP, in part by controlling inflammation and hyperproliferation of other cells.

In vivo edited eosinophils reconcile antigen specific Th2 response and mitigate airway allergy

BACKGROUND

Improvement is needed in the remedies used to control Th2 polarization. Bioengineering approaches have modified immune cells that have immunosuppressive functions. This study aims to generate modified eosinophils (Meos) in vivo and use Meos to balance Th2 polarization and reduce airway allergy.

METHODS

A cell editor was constructed. The editor contained a peptide carrier, an anti-siglec F antibody, MHC II, ovalbumin, and LgDNA (DNA extracted from a probiotic, Lactobacillus rhamnosus GG). Which was designated as Cedit. Meos are eosinophils modified using Cedits. An airway Th2 polarization mouse model was established used to test the effect of Meos on suppressing airway allergy.

RESULTS

The Cedits remained physically and chemically stable in solution (pH7.2) for at least 96 h. Cedits specifically bound to eosinophils, which are designated as Meos. Meos produced programmed death ligand-1 (PD-L1); the latter induced antigen specific CD4+ T cell apoptosis. Administration of Cedits through nasal instillations generated Meos in vivo, which significantly reduced the frequency of antigen specific CD4+ T cells in the airways, and mitigated airway Th2 polarization.

CONCLUSIONS

We constructed Cedit, which could edit eosinophils into Meos in vivo. Meos could induce antigen specific CD4+ T cell apoptosis, and reconcile airway Th2 polarization.

Regulation of intestinal epithelial homeostasis by mesenchymal cells

The gastrointestinal tract harbors diverse microorganisms in the lumen. Epithelial cells segregate the luminal microorganisms from immune cells in the lamina propria by constructing chemical and physical barriers through the production of various factors to prevent excessive immune responses against microbes. Therefore, perturbations of epithelial integrity are linked to the development of gastrointestinal disorders. Several mesenchymal stromal cell populations, including fibroblasts, myofibroblasts, pericytes, and myocytes, contribute to the establishment and maintenance of epithelial homeostasis in the gut through regulation of the self-renewal, proliferation, and differentiation of intestinal stem cells. Recent studies have revealed alterations in the composition of intestinal mesenchymal stromal cells in patients with inflammatory bowel disease and colorectal cancer. A better understanding of the interplay between mesenchymal stromal cells and epithelial cells associated with intestinal health and diseases will facilitate identification of novel biomarkers and therapeutic targets for gastrointestinal disorders. This review summarizes the key findings obtained to date on the mechanisms by which functionally distinct mesenchymal stromal cells regulate epithelial integrity in intestinal health and diseases at different developmental stages.

Antibiotic use during influenza infection augments lung eosinophils that impair immunity against secondary bacterial pneumonia

A leading cause of mortality after influenza infection is the development of a secondary bacterial pneumonia. In the absence of a bacterial superinfection, prescribing antibacterial therapies is not indicated but has become a common clinical practice for those presenting with a respiratory viral illness. In a murine model, we found that antibiotic use during influenza infection impaired the lung innate immunologic defenses toward a secondary challenge with methicillin-resistant Staphylococcus aureus (MRSA). Antibiotics augment lung eosinophils, which have inhibitory effects on macrophage function through the release of major basic protein. Moreover, we demonstrated that antibiotic treatment during influenza infection caused a fungal dysbiosis that drove lung eosinophilia and impaired MRSA clearance. Finally, we evaluated 3 cohorts of hospitalized patients and found that eosinophils positively correlated with antibiotic use, systemic inflammation, and worsened outcomes. Altogether, our work demonstrates a detrimental effect of antibiotic treatment during influenza infection that has harmful immunologic consequences via recruitment of eosinophils to the lungs, thereby increasing the risk of developing a secondary bacterial infection.

Eosinophils as drivers of bacterial immunomodulation and persistence

Traditionally, eosinophils have been linked to parasitic infections and pathological disease states. However, emerging literature has unveiled a more nuanced and intricate role for these cells, demonstrating their key functions in maintaining mucosal homeostasis. Eosinophils exhibit diverse phenotypes and exert multifaceted effects during infections, ranging from promoting pathogen persistence to triggering allergic reactions. Our investigations primarily focus on Bordetella spp., with particular emphasis on Bordetella bronchiseptica, a natural murine pathogen that induces diseases in mice akin to pertussis in humans. Recent findings from our published work have unveiled a striking interaction between B. bronchiseptica and eosinophils, facilitated by the btrS-mediated mechanism. This interaction serves to enhance pathogen persistence while concurrently delaying adaptive immune responses. Notably, this role of eosinophils is only noted in the absence of a functional btrS signaling pathway, indicating that wild-type B. bronchiseptica, and possibly other Bordetella spp., possess such adeptness in manipulating eosinophils that the true function of these cells remains obscured during infection. In this review, we present the mounting evidence pointing toward eosinophils as targets of bacterial exploitation, facilitating pathogen persistence and fostering chronic infections in diverse mucosal sites, including the lungs, gut, and skin. We underscore the pivotal role of the master regulator of Bordetella pathogenesis, the sigma factor BtrS, in orchestrating eosinophil-dependent immunomodulation within the context of pulmonary infection. These putative convergent strategies of targeting eosinophils offer promising avenues for the development of novel therapeutics targeting respiratory and other mucosal pathogens.

Does Eosinophil Heterogeneity Translate into Functional Diversity? A Review of the Evolving Paradigm of Eosinophil Heterogeneity in Asthma

This review provides an overview of evidence supporting the existence of distinct homeostatic and inflammatory eosinophil subpopulations in health and disease. Particular emphasis is placed on describing the phenotypic and functional roles of these eosinophil subtypes in asthma, as well as the phenotypic changes induced by clinical therapy with the anti-IL-5 biologic agent, mepolizumab. Improved understanding of distinct eosinophil phenotypes may enable targeting of select subpopulations in the treatment of patients with type 2 inflammatory diseases such as asthma.

Host-pathogen interactions from a metabolic perspective: methods of investigation

Metabolism shapes immune homeostasis in health and disease. This review presents the range of methods that are currently available to investigate the dialog between metabolism and immunity at the systemic, tissue and cellular levels, particularly during infection.

TGF-β signaling promotes eosinophil activation in inflammatory responses

Eosinophils, traditionally associated with allergic phenomena, play a pivotal role in inflammatory responses. Despite accumulating evidence suggesting their pro-inflammatory function upon activation, the underlying mechanisms governing eosinophil activation remain incompletely characterized. In this study, we investigate the local activation of pulmonary and colon eosinophils within the inflammatory microenvironment. Leveraging transcriptional sequencing, we identify TGF-β as a putative regulator of eosinophil activation, leading to the secretion of granule proteins, including peroxidase. Genetic deletion of TGF-β receptors on eosinophils resulted in the inhibition of peroxidase synthesis, affirming the significance of TGF-β signaling in eosinophil activation. Using models of HDM-induced asthma and DSS-induced colitis, we demonstrate the indispensability of TGF-β-driven eosinophil activation in both disease contexts. Notably, while TGF-β signaling did not significantly influence asthmatic inflammation, its knockout conferred protection against experimental colitis. This study delineates a distinct pattern of eosinophil activation within inflammatory responses, highlighting the pivotal role of TGF-β signaling in regulating eosinophil behavior. These findings deepen our comprehension of eosinophil-related pathophysiology and may pave the way for targeted therapeutic approaches in allergic and inflammatory diseases.

Stromal cell and B cell dialogue potentiates IL-33-enriched lymphoid niches to support eosinophil recruitment and function during type 2 immunity

Eosinophils are involved in host protection against multicellular organisms. However, their recruitment to the mesenteric lymph node (mLN) during type 2 immunity is understudied. Our results demonstrate that eosinophil association with lymphoid stromal niches constructed by fibroblastic reticular cells (FRCs) and lymphatic endothelial cells is diminished in mice selectively lacking interleukin (IL)-4Rα or lymphotoxin-β (LTβ) expression on B cells. Furthermore, eosinophil survival, activation, and enhanced Il1rl1 receptor expression are driven by stromal cell and B cell dialogue. The ligation of lymphotoxin-β receptor (LTβR) on FRCs improves eosinophil survival and significantly augments IL-33 expression and eosinophil homing to the mLN, thus confirming the significance of lymphotoxin signaling for granulocyte recruitment. Eosinophil-deficient ΔdblGATA-1 mice show diminished mLN expansion, reduced interfollicular region (IFR) alarmin expression, and delayed helminth clearance, elucidating their importance in type 2 immunity. These findings provide insight into dialogue between stromal cells and B cells, which govern mLN eosinophilia, and the relevance of these mechanisms during type 2 immunity.

IL-5 antagonism reverses priming and activation of eosinophils in severe eosinophilic asthma

Eosinophils are key effector cells mediating airway inflammation and exacerbation in patients with severe eosinophilic asthma. They are present in increased numbers and activation states in the airway mucosa and lumen. Interleukin-5 (IL-5) is the key eosinophil growth factor that is thought to play a role in eosinophil priming and activation. However, the mechanism of these effects is still not fully understood. The anti-IL-5 antibody mepolizumab reduces eosinophil counts in the airway modestly but has a large beneficial effect on the frequency of exacerbations of severe eosinophilic asthma, suggesting that reduction in eosinophil priming and activation is of central mechanistic importance. In this study, we used the therapeutic effect of mepolizumab and single-cell ribonucleic acid sequencing to investigate the mechanism of eosinophil priming and activation by IL-5. We demonstrated that IL-5 is a dominant driver of eosinophil priming and plays multifaceted roles in eosinophil function. It enhances eosinophil responses to other stimulators of migration, survival, and activation by activating phosphatidylinositol-3-kinases, extracellular signal-regulated kinases, and p38 mitogen-activated protein kinases signaling pathways. It also enhances the pro-fibrotic roles of eosinophils in airway remodeling via transforming growth factor-β pathway. These findings provide a mechanistic understanding of eosinophil priming in severe eosinophilic asthma and the therapeutic effect of anti-IL-5 approaches in the disease.

Helminth infection driven gastrointestinal hypermotility is independent of eosinophils and mediated by alterations in smooth muscle instead of enteric neurons

Intestinal helminth infection triggers a type 2 immune response that promotes a 'weep-and sweep' response characterised by increased mucus secretion and intestinal hypermotility, which function to dislodge the worm from its intestinal habitat. Recent studies have discovered that several other pathogens cause intestinal dysmotility through major alterations to the immune and enteric nervous systems (ENS), and their interactions, within the gastrointestinal tract. However, the involvement of these systems has not been investigated for helminth infections. Eosinophils represent a key cell type recruited by the type 2 immune response and alter intestinal motility under steady-state conditions. Our study aimed to investigate whether altered intestinal motility driven by the murine hookworm, Nippostrongylus brasiliensis, infection involves eosinophils and how the ENS and smooth muscles of the gut are impacted. Eosinophil deficiency did not influence helminth-induced intestinal hypermotility and hypermotility did not involve gross structural or functional changes to the ENS. Hypermotility was instead associated with a dramatic increase in smooth muscle thickness and contractility, an observation that extended to another rodent nematode, Heligmosomoides polygyrus. In summary our data indicate that, in contrast to other pathogens, helminth-induced intestinal hypermotility is driven by largely by myogenic, rather than neurogenic, alterations with such changes occurring independently of eosinophils. (<300 words).

Notch 2 signaling contributes to intestinal eosinophil adaptations in steady state and tissue burden following oral allergen challenge

Eosinophils not only function as inflammatory effectors in allergic diseases, but also contribute to tissue homeostasis in steady state. Emerging data are revealing tissue eosinophils to be adaptive cells, imprinted by their local tissue microenvironment and exhibiting distinct functional phenotypes that may contribute to their homeostatic vs. inflammatory capacities. However, signaling pathways that regulate eosinophil tissue adaptations remain elusive. Notch signaling is an evolutionarily conserved pathway that mediates differential cell fate programming of both pre- and postmitotic immune cells. This study investigated a role for notch receptor 2 signaling in regulating eosinophil functions and tissue phenotype in both humans and mice. Notch 2 receptors were constitutively expressed and active in human blood eosinophils. Pharmacologic neutralization of notch 2 in ex vivo stimulated human eosinophils altered their activated transcriptome and prevented their cytokine-mediated survival. Genetic ablation of eosinophil-expressed notch 2 in mice diminished steady-state intestine-specific eosinophil adaptations and impaired their tissue retention in a food allergic response. In contrast, notch 2 had no effect on eosinophil phenotype or tissue inflammation within the context of allergic airways inflammation, suggesting that notch 2-dependent regulation of eosinophil phenotype and function is specific to the gut. These data reveal notch 2 signaling as a cell-intrinsic mechanism that contributes to eosinophil survival, function, and intestine-specific adaptations. The notch 2 pathway may represent a viable strategy to reprogram eosinophil functional phenotypes in gastrointestinal eosinophil-associated diseases.

Eosinophils exhibit a unique transcriptional signature and increased sensitivity to IL-3-induced activation in response to colorectal cancer cells

Eosinophils have been mainly studied in allergic diseases and parasitic infections. Nonetheless, eosinophils accumulate in a variety of solid tumors, including colorectal cancer, where their presence is associated with improved prognosis. Eosinophils can promote antitumor immunity through various mechanisms, including direct cytotoxicity toward tumor cells and promoting T-cell activation. However, the mechanisms by which tumor cells regulate eosinophil activities are largely unknown. Herein, we characterized the potential interactions between eosinophils and colorectal cancer cells using an unbiased transcriptomic and proteomic analyses approach. Human eosinophils were stimulated with colorectal cancer cell conditioned media, containing tumor cell secreted factors from multiple cancer cell lines. RNA sequencing analysis identified a "core" signature consisting of 101 genes that characterize a baseline transcriptional program for the response of human eosinophils to colorectal cancer cells. Among these, the increased expression of IL-3Rα and its βc chain was identified and validated at the protein level. Secreted factors from tumor cells potentiated IL-3-induced expression of the adhesion molecule CD11a in eosinophils. Combining proteomics analysis of tumor cell secreted factors with RNA sequencing revealed potential ligand-receptor pairs between tumor cells and eosinophils and the potential involvement of the adhesion molecule CD18 and F2RL3/PAR4. Subsequent functional analyses demonstrated that F2RL3/PAR4 suppresses eosinophil migration in response tumor cell secreted factors. These findings add to the growing body of evidence that eosinophils are conditioned by their local microenvironment. Identifying mechanisms by which eosinophils interact with tumor cells could lead to the development of new immunotherapies for colorectal cancer and other solid tumors.

The AHR repressor limits expression of antimicrobial genes but not AHR-dependent genes in intestinal eosinophils

Intestinal eosinophils express the aryl hydrocarbon receptor (AHR), an environmental sensor and ligand-activated transcription factor that responds to dietary or environmental ligands. AHR regulates tissue adaptation, survival, adhesion, and immune functions in intestinal eosinophils. The AHR repressor (AHRR) is itself induced by AHR and believed to limit AHR activity in a negative feedback loop. We analyzed gene expression in intestinal eosinophils from wild-type and AHRR knockout mice and found that AHRR did not suppress most AHR-dependent genes. Instead, AHRR limited the expression of a distinct small set of genes involved in the innate immune response. These included S100 proteins, antimicrobial proteins, and alpha-defensins. Using bone marrow-derived eosinophils, we found that AHRR knockout eosinophils released more reactive oxygen species upon stimulation. This work shows that the paradigm of AHRR as a repressor of AHR transcriptional activity does not apply to intestinal eosinophils. Rather, AHRR limits the expression of innate immune response and antimicrobial genes, possibly to maintain an anti-inflammatory phenotype in eosinophils when exposed to microbial signals in the intestinal environment.

Eosinophil expression of triggering receptor expressed on myeloid cells 1 (TREM-1) restricts type 2 lung inflammation

Asthma affects 25 million Americans, and recent advances in treatment are effective for only a portion of severe asthma patients. TREM-1, an innate receptor that canonically amplifies inflammatory signaling in neutrophils and monocytes, plays a central role in regulating lung inflammation. It is unknown how TREM-1 contributes to allergic asthma pathology. Utilizing a murine model of asthma, flow cytometry revealed TREM-1+ eosinophils in the lung tissue and airway during allergic airway inflammation. TREM-1 expression was restricted to recruited, inflammatory eosinophils. Expression was induced on bone marrow-derived eosinophils by incubation with interleukin 33, lipopolysaccharide, or granulocyte-macrophage colony-stimulating factor. Compared to TREM-1- airway eosinophils, TREM-1+ eosinophils were enriched for proinflammatory gene sets, including migration, respiratory burst, and cytokine production. Unexpectedly, eosinophil-specific ablation of TREM-1 exacerbated airway interleukin (IL) 5 production, airway MUC5AC production, and lung tissue eosinophil accumulation. Further investigation of transcriptional data revealed apoptosis and superoxide generation-related gene sets were enriched in TREM-1+ eosinophils. Consistent with these findings, annexin V and caspase-3/7 staining demonstrated higher rates of apoptosis among TREM-1+ eosinophils compared to TREM-1- eosinophils in the inflammatory airway. In vitro, Trem1/3-/- bone marrow-derived eosinophils consumed less oxygen than wild-type in response to phorbol myristate acetate, suggesting that TREM-1 promotes superoxide generation in eosinophils. These data reveal protein-level expression of TREM-1 by eosinophils, define a population of TREM-1+ inflammatory eosinophils, and demonstrate that eosinophil TREM-1 restricts key features of type 2 lung inflammation.

Ally, adversary, or arbitrator? The context-dependent role of eosinophils in vaccination for respiratory viruses and subsequent breakthrough infections

Eosinophils are a critical type of immune cell and central players in type 2 immunity. Existing literature suggests that eosinophils also can play a role in host antiviral responses, typically type 1 immune events, against multiple respiratory viruses, both directly through release of antiviral mediators and indirectly through activation of other effector cell types. One way to prime host immune responses toward effective antiviral responses is through vaccination, where typically a type 1-skewed immunity is desirable in the context of intracellular pathogens like respiratory viruses. In the realm of breakthrough respiratory viral infection in vaccinated hosts, an event in which virus can still establish productive infection despite preexisting immunity, eosinophils are most prominently known for their link to vaccine-associated enhanced respiratory disease upon natural respiratory syncytial virus infection. This was observed in a pediatric cohort during the 1960s following vaccination with formalin-inactivated respiratory syncytial virus. More recent research has unveiled additional roles of the eosinophil in respiratory viral infection and breakthrough infection. The specific contribution of eosinophils to the quality of vaccine responses, vaccine efficacy, and antiviral responses to infection in vaccinated hosts remains largely unexplored, especially regarding their potential roles in protection. On the basis of current findings, we will speculate upon the suggested function of eosinophils and consider the many potential ways by which eosinophils may exert protective and pathological effects in breakthrough infections. We will also discuss how to balance vaccine efficacy with eosinophil-related risks, as well as the use of eosinophils and their products as potential biomarkers of vaccine efficacy or adverse events.