Chronic systemic inflammation and DNA methylation changes are two major hallmarks of aging, yet their interaction is poorly known. We investigated the relation between circulating inflammatory proteome and epigenetic age acceleration as assessed by DNA methylation in four independent cohorts of different ages and health conditions. Epigenetic age scores known to predict human health span (GrimAge and PhenoAge) were more strongly associated with age-associated inflammatory proteins, frailty, and multimorbidity when compared to epigenetic age scores associated with lifespan (Horvath and Hannum). Mendelian randomization analyses showed that blood concentrations of important inflammatory cytokines associated with the interferon pathway (CXCL9, CXCL10, CCL11, and IL-18) increase with age and are causal drivers of epigenetic age acceleration and age-related diseases. Furthermore, aging was associated with dysregulation of cytokine production capacity in immune cells in response to microbial stimulation. These findings argue that the interferon pathway may represent a target for anti-aging interventions.

Aims: Trained immunity, defined as long-term functional reprogramming of innate immune cells, has been implicated in the heterologous protective effects of certain vaccines against infection and cancer. AS01-adjuvanted vaccines have been suggested to provide such heterologous protective effects. We therefore aimed to investigate the capacity of AS01 to induce trained immunity and evaluated its potential as an antitumoral therapeutic. Methods: Acute cytokine production was assessed in human monocytes after AS01 stimulation. Trained immunity was subsequently evaluated by interleukin-6 (IL-6) and tumor necrosis factor (TNF) quantification following heterologous restimulation. Antitumor efficacy of AS01 was assessed in mice bearing B16-F10 melanoma, MB49 bladder cancer, or Lewis lung carcinoma by monitoring tumor growth. Immune phenotyping of B16-F10 and MB49 tumor microenvironments was determined with flow cytometry. Results: Although AS01 did not stimulate acute inflammation, it induced trained immunity, marked by increased responsiveness upon secondary stimulation in human monocytes. Treatment of mice bearing B16-F10 melanoma or MB49 bladder cancer with AS01 strongly diminished tumor growth, whereas no effect was observed in the Lewis lung carcinoma model. In these responsive models, the antitumor effects of AS01 were associated with an altered tumor microenvironment, characterized by increased infiltration of CD8+ T cells, regulatory T cells, neutrophils, and monocytes, along with a decrease in tumor-associated macrophages. AS01 also decreased expression of immune checkpoint protein PD-L1 in monocytes and neutrophils, suggesting enhanced antitumor immune responsiveness. Conclusion: Our findings show the capacity of AS01 to induce trained immunity and support its potential to be repurposed as an immunotherapeutic approach for cancer.

Host-respiratory microbiome interplay is vital to lung homeostasis. Systemic inflammatory response syndrome (SIRS) is an intense alteration in host status that necessitates rapid microbiome adaptation to avoid respiratory complications. Using longitudinal multi-omic data from patients with SIRS, we confirm that the respiratory microbiome, blood metabolome, and immune cells form a dynamic metasystem and define a metacluster with distinct T/B cell trafficking, anaerobic bacteria, high tyrosine metabolism, and low fatty acid biosynthesis. This metacluster status can serve to classify the severity of alterations in host-lung microbiome interactions as moderate or severe and to predict pneumonia and mortality. We demonstrate the robustness of these findings in an independent, randomized controlled trial and propose that interferon-γ treatment may benefit patients with severe metacluster alterations but harm those with moderate alterations. Our study supports the concept of the host-respiratory microbiome as a dynamic metasystem, in which specific alterations are associated with pneumonia and responses to interferon-γ treatment.

Trained immunity, also termed innate immune memory, is supported by the metabolic rewiring of innate immune cells, altering their bioenergetic profile and ultimately their functions. While amino acids such as arginine are known to possess immunomodulatory properties, their role in trained immunity remains largely unexplored. Primary human monocytes were trained with β-glucan in a medium enriched with or deprived of arginine or supplemented with an arginase inhibitor. After a resting period, trained cells were restimulated with LPS. Arginine deprivation or arginase inhibition during β-glucan training impaired the amplification of IL-6 and TNF cytokine response to LPS, while they did not affect the cells' phagocytotic capacity. Arginine deprivation also significantly reduced the oxygen consumption rate of trained cells, without affecting glycolysis. Genetic studies revealed polymorphisms near genes coding for arginine-metabolizing enzymes modulated the induction of trained immunity, highlighting the role of arginine-derived metabolites in trained immunity. These findings demonstrate that arginine and its metabolites are involved in the induction of trained immunity. Understanding metabolic mechanisms involved in trained immunity could provide insights into new therapeutic strategies for harnessing arginine deprivation to modulate inflammatory disorders.

Trained immunity, a de facto innate immune memory characterized by enhanced responsiveness to future challenges, is underpinned by epigenetic and metabolic rewiring. In individuals vaccinated with Bacille Calmette-Guérin (BCG), lactate release was associated with enhanced cytokine responsiveness upon restimulation. Trained monocytes/macrophages are characterized by lactylation of histone H3 at lysine residue 18(H3K18la), mainly at distal regulatory regions. Histone lactylation was positively associated with active chromatin and gene transcription, persisted after the elimination of the training stimulus, and was strongly associated with "trained" gene transcription in response to a secondary stimulus. Increased lactate production upon induction of trained immunity led to enhanced production of proinflammatory cytokines, a process associated with histone lactylation. Pharmacological inhibition of lactate production or histone lactylation blocked trained immunity responses, while polymorphisms of LDHA and EP300 genes modulated trained immunity. Long-term histone lactylation persisted in vivo 90 days after vaccination with BCG, highlighting H3K18la as an epigenetic mark of innate immune memory.

Infections, cancer, and trauma can cause life-threatening hyperinflammation. In the present study, using single-cell RNA sequencing of circulating immune cells, we found that the mammalian target of rapamycin (mTOR) pathway plays a critical role in myeloid cell regulation in COVID-19 patients. Previously, we developed an mTOR-inhibiting nanobiologic (mTORi-nanobiologic) that efficiently targets myeloid cells and their progenitors in the bone marrow. In vitro, we demonstrated that mTORi-nanobiologics potently inhibit infection-associated inflammation in human primary immune cells. Next, we investigated the in vivo effect of mTORi-nanobiologics in mouse models of hyperinflammation and acute respiratory distress syndrome. Using 18F-FDG uptake and flow cytometry readouts, we found mTORi-nanobiologic therapy to efficiently reduce hematopoietic organ metabolic activity and inflammation to levels comparable to those of healthy control animals. Together, we show that regulating myelopoiesis with mTORi-nanobiologics is a compelling therapeutic strategy to prevent deleterious organ inflammation in infection-related complications.

Post-Acute COVID-19 syndrome (PACS) is heterogeneous in phenotype and functional state. This prospective, observational study studied adults six months after acute COVID-19. We defined clinical phenotypes and profiled plasma mediators grouped into functional pathways (IL-1, IL-17, IFNγ/IFNγ-related cytokines, pro-/anti-inflammatory clusters). A subset underwent RNA-seq and ChIP-seq experiments. Three cohorts were analyzed (Exploratory n = 46; Discovery n = 591; Validation Cohort n = 289). PACS compatible symptoms were identified in 69.6 %; 59.2 % and 54.7 % respectively. Five phenotypes emerged. IL-1 cytokines (OR: 3.17, 95 % CIs: 1.94-5.19, p: 4.5 × 10-6), IL-17 cytokines (OR: 2.45, 95 % CIs: 1.47-4.07 p: 5.88 × 10-4) and the anti-inflammatory biomarkers (OR: 2.15, 95 % CIs: 1.34-3.45, p: 1.5 × 10-3) were upregulated in PACS patients. Respiratory phenotype was correlated with IL-1 upregulation (OR 4.23; 95 % CIs, 1.69-10.8, p = 0.0025). Transcriptomic and epigenomic changes were observed. Distinct phenotypes of PACS are driven by different immunological mechanisms at the DNA, transcriptomic, and protein levels.

The innate immune system adapts its behavior based on previous insults, mounting an enhanced response upon re-exposure. Hematopoietic progenitors in the bone marrow and peripheral innate immune cells can undergo epigenetic and metabolic reprogramming, establishing an innate immune memory known as trained immunity. The concept of trained immunity recently gained relevance in our understanding of how innate immunity is regulated in various diseases. This review explores the role of trained immunity in infections, autoimmune disease, cardiovascular disease, cancer, and neurodegenerative disease. We discuss how trained immunity can provide heterologous protection against infections, as it has been induced for decades by the Bacillus Calmette Guérin vaccine, how it can help counteract immunosuppression, and how it can be inappropriately induced leading to chronic inflammation. By understanding how trained immunity is involved in processes leading to health and disease, novel therapeutic strategies can be developed.

Trained immunity induces antigen-agnostic enhancement of host defense and protection against secondary infections, but inappropriate activation can contribute to the pathophysiology of inflammatory diseases. Tight regulation of trained immunity is therefore needed to avoid pathology, but little is known about the endogenous processes that modulate it. Here, we investigated the potential of interleukin (IL)-10, a prototypical anti-inflammatory cytokine, to inhibit trained immunity. IL-10 induced tolerance and inhibited trained immunity in primary human monocytes at both functional and transcriptional levels. Inhibition of STAT3, a signaling route that mediates IL-10 signals, induced trained immunity. IL-10 downregulated glycolytic and oxidative metabolism in monocytes but did not impact the metabolic effects of β-glucan-induced trained immunity. Furthermore, IL-10 prevented increased reactive oxygen species production in Bacillus Calmette-Guérin (BCG)-induced training but did not influence phagocytosis upregulation. In a cohort study of healthy volunteers vaccinated with BCG, genetic variants that influenced IL-10 or its receptor modulated BCG-induced trained immunity. Furthermore, circulating IL-10 concentrations were negatively correlated with induction of trained immunity after BCG vaccination in a sex-specific manner. In conclusion, IL-10 inhibited several, albeit not all, immunological functions amplified after induction of trained immunity. Follow-up studies should explore the precise molecular mechanism that mediates the effects of IL-10 on trained immunity. Addressing these knowledge gaps is an important step toward optimizing IL-10's potential as a therapeutic target in diseases characterized by inappropriate induction of trained immunity.

Dysregulation and hyperactivation of innate immune responses can lead to the onset of systemic autoinflammatory diseases. Monogenic autoinflammatory diseases are caused by inborn genetic errors and based on molecular mechanisms at play, can be divided into inflammasomopathies, interferonopathies, relopathies, protein misfolding, and endogenous antagonist deficiencies. On the other hand, more common autoinflammatory diseases are multifactorial, with both genetic and non-genetic factors playing an important role. During the last decade, long-term memory characteristics of innate immune responses have been described (also called trained immunity) that in physiological conditions provide enhanced host protection from pathogenic re-infection. However, if dysregulated, induction of trained immunity can become maladaptive, perpetuating chronic inflammatory activation. Here, we describe the mechanisms of genetic and epigenetic dysregulation of the innate immune system and maladaptive trained immunity that leads to the onset and perpetuation of the most common and recently described systemic autoinflammatory diseases.

OBJECTIVES:IL-1α/β and TNF are closely linked to the pathology of severe COVID-19 and sepsis. The soluble forms of their receptors, functioning as decoy receptors, exhibit inhibitory effects. However, little is known about their regulation in severe bacterial and viral infections, which we aimed to investigate in this study. METHODS:The circulating soluble receptors of TNF (sTNFR1 and sTNFR2) and IL-1α/β (sIL-1R1, sIL-1R2) were evaluated in the plasma of patients with COVID-19, severe bacterial infections, and sepsis and compared with healthy controls. Additionally, IL1R1, IL1R2, TNFRSF1A, and TNFRSF1B expression was evaluated at the single cell level in PBMCs derived from COVID-19 or sepsis patients. RESULTS:Plasma concentrations of sIL-1R1, sTNFR1, and sTNFR2 were significantly higher in COVID-19 patients compared to healthy subjects. Notably, sIL-1R1 levels were particularly elevated in ICU COVID-19 patients, and transcriptome analysis indicated heightened IL1R1 expression in PBMCs from severe COVID-19 patients. In severe bacterial infections, only sTNFR1 and sTNFR2 exhibited increased levels compared to healthy controls. Sepsis patients had decreased sIL-1R1 plasma concentrations but elevated sIL-1R2, sTNFR1, and sTNFR2 levels compared to healthy individuals, reflecting the heightened expression due to the increased numbers of monocytes present in sepsis. Finally, elevated concentrations of sIL-1R2, sTNFR1, and sTNFR2 were moderately associated with reduced 28-day survival in sepsis patients. CONCLUSION:Our study reveals distinct regulation of plasma concentrations of soluble IL-1 receptors in COVID-19 and sepsis. Moreover, soluble TNF receptors 1 and 2 consistently rise in all conditions and show a positive correlation with disease severity in sepsis.

OBJECTIVETrained immunity (TI) is a de facto memory program of innate immune cells, characterized by immunometabolic and epigenetic changes sustaining enhanced production of cytokines. TI evolved as a protective mechanism against infections; however, inappropriate activation can cause detrimental inflammation and might be implicated in the pathogenesis of chronic inflammatory diseases. In this study, we investigated the role of TI in the pathogenesis of giant cell arteritis (GCA), a large-vessel vasculitis characterized by aberrant macrophage activation and excess cytokine production.METHODSMonocytes from GCA patients and from age- and sex-matched healthy donors were subjected to polyfunctional studies, including cytokine production assays at baseline and following stimulation, intracellular metabolomics, chromatin immunoprecipitation-qPCR, and combined ATAC/RNA sequencing. Immunometabolic activation (i.e. glycolysis) was assessed in inflamed vessels of GCA patients with FDG-PET and immunohistochemistry (IHC), and the role of this pathway in sustaining cytokine production was confirmed with selective pharmacologic inhibition in GCA monocytes.RESULTSGCA monocytes exhibited hallmark molecular features of TI. Specifically, these included enhanced IL-6 production upon stimulation, typical immunometabolic changes (e.g. increased glycolysis and glutaminolysis) and epigenetic changes promoting enhanced transcription of genes governing pro-inflammatory activation. Immunometabolic changes of TI (i.e. glycolysis) were a feature of myelomonocytic cells in GCA lesions and were required for enhanced cytokine production.CONCLUSIONSMyelomonocytic cells in GCA activate TI programs sustaining enhanced inflammatory activation with excess cytokine production.

Trained immunity is a long-term increase in responsiveness of innate immune cells, induced by certain infections and vaccines. During the last 3 years of the COVID-19 pandemic, vaccines that induce trained immunity, such as BCG, MMR, OPV, and others, have been investigated for their capacity to protect against COVID-19. Further, trained immunity-inducing vaccines have been shown to improve B and T cell responsiveness to both mRNA- and adenovirus-based anti-COVID-19 vaccines. Moreover, SARS-CoV-2 infection itself induces inappropriately strong programs of trained immunity in some individuals, which may contribute to the long-term inflammatory sequelae. In this review, we detail these and other aspects of the role of trained immunity in SARS-CoV-2 infection and COVID-19. We also examine the learnings from the trained immunity studies conducted in the context of this pandemic and discuss how they may help us in preparing for future infectious outbreaks.

BackgroundDexamethasone improves the survival of COVID-19 patients in need of supplemental oxygen therapy. Although its broad immunosuppressive effects are well-described, the immunological mechanisms modulated by dexamethasone in patients hospitalized with COVID-19 remain to be elucidated.ObjectiveWe combined functional immunological assays and an omics-based approach to investigate the in vitro and in vivo effects of dexamethasone in the plasma and peripheral blood mononuclear cells (PBMCs) of COVID-19 patients.MethodsHospitalized COVID-19 patients eligible for dexamethasone therapy were recruited from the general care ward between February and July, 2021. Whole blood transcriptomic and targeted plasma proteomic analyses were performed before and after starting dexamethasone treatment. PBMCs were isolated from healthy individuals and COVID-19 patients and stimulated with inactivated SARS-CoV-2 ex vivo in the presence or absence of dexamethasone and transcriptome and cytokine responses were assessed.ResultsDexamethasone efficiently inhibited SARS-CoV-2-induced in vitro expression of chemokines and cytokines in PBMCs at the transcriptional and protein level. Dexamethasone treatment in COVID-19 patients resulted in down-regulation of genes related to type I and II interferon (IFN) signaling in whole blood immune cells. In addition, dexamethasone attenuated circulating concentrations of secreted interferon-stimulating gene 15 (ISG15) and pro-inflammatory cytokines and chemokines correlating with disease severity and lethal outcomes, such as tumor necrosis factor (TNF), interleukin-6 (IL-6), chemokine ligand 2 (CCL2), C-X-C motif ligand 8 (CXCL8), and C-X-C motif chemokine ligand 10 (CXCL10). In PBMCs from COVID-19 patients that were stimulated ex vivo with multiple pathogens or Toll-like receptor (TLR) ligands, dexamethasone efficiently inhibited cytokine responses.ConclusionWe describe the anti-inflammatory impact of dexamethasone on the pathways contributing to cytokine hyperresponsiveness observed in severe manifestations of COVID-19, including type I/II IFN signaling. Dexamethasone could have adverse effects in COVID-19 patients with mild symptoms by inhibiting IFN responses in early stages of the disease, whereas it exhibits beneficial effects in patients with severe clinical phenotypes by efficiently diminishing cytokine hyperresponsiveness.

Infections and vaccines can induce enhanced long-term responses in innate immune cells, establishing an innate immunological memory termed trained immunity . Here, we show that monocytes with a trained immunity phenotype, due to exposure to the Bacillus Calmette-Guérin (BCG) vaccine, are characterized by an increased biosynthesis of different lipid mediators (LM) derived from long-chain polyunsaturated fatty acids (PUFA). Pharmacological and genetic approaches show that long-chain PUFA synthesis and lipoxygenase-derived LM are essential for the BCG-induced trained immunity responses of human monocytes. Furthermore, products of 12-lipoxygenase activity increase in monocytes of healthy individuals after BCG vaccination. Grasping the underscoring lipid metabolic pathways contributes to our understanding of trained immunity and may help to identify therapeutic tools and targets for the modulation of innate immune responses.

Trained immunity is a de facto memory for innate immune responses, leading to long-term functional reprogramming of innate immune cells. In physiological conditions, trained immunity leads to adaptive states that enhance resistance against pathogens and contributes to immunosurveillance. Dysregulated trained immunity can however lead either to defective innate immune responses in severe infections or cancer or to inflammatory and autoimmune diseases if trained immunity is inappropriately activated. Here, we review the immunological and molecular mechanisms that mediate trained immunity induction and propose that trained immunity represents an important target for prophylactic and therapeutic approaches in human diseases. On the one hand, we argue that novel approaches that induce trained immunity may enhance vaccine efficacy. On the other hand, induction of trained immunity in cancer, and inhibition of exaggerated induction of trained immunity in inflammatory disorders, are viable targets amenable for new therapeutic approaches.

IntroductionTrained Immunity represents a novel revolutionary concept of the immunological response involving innate immune cells. Bisphenol A is a well-known endocrine disrupter, widely disseminated worldwide and accumulated in the human body. Due to the increased interest regarding the effects of plastic-derived compounds on the immune system, our purpose was to explore whether BPA was able to induce trained immunity in human primary monocytes in vitro using low environmental concentrations.Materials and methodsWe extracted BPA from the serum of 10 healthy individuals through a liquid-liquid extraction followed by a solid phase extraction and measured the concentration using an HPLC system coupled to a triple quadrupole mass spectrometer. In parallel, monocytes were isolated from whole blood and acutely stimulated or trained with BPA at three different concentrations (1 nM, 10 nM, 20 nM). Pro- and anti-inflammatory cytokines (IL-1β, TNF-α, IL-6, and IL-10) production were assessed after 24 hours of acute stimulation and after Lipopolysaccharide (LPS) rechallenge. A comprehensive overview of the metabolic changes after BPA acute stimulation and trained immunity induction was assessed through extracellular lactate measurements, Seahorse XFb metabolic flux analysis and ROS production.ResultsMonocytes primed with BPA showed increased pro- and anti-inflammatory cytokine responses upon restimulation, sustained by the modulation of the immunometabolic circuits. Moreover, we proved the non-toxic effect of BPA at each experimental concentration by performing an MTT assay. Additionally, correlation analysis were performed between pro- and anti-inflammatory cytokines production after LPS acute stimulation or BPA-mediated trained immunity and BPA serum concentrations showing a significant association between TNF-α and BPA circulating levels.DiscussionOverall, this study pointed out for the first time the immunological effects of an environmental chemical and plastic-derived compound in the induction of trained immunity in a healthy cohort.

We studied whether progression of severe pneumonia into post-acute COVID-19 syndrome (PACS) is associated with long-term immune dysregulation. Patients with known history of COVID-19 pneumonia during two different time periods and matched comparators were divided into a discovery cohort (n=46, September-October 2020) and a validation cohort (n=484, June-August 2021). Peripheral blood mononuclear cells (PBMCs) were stimulated for cytokine production, patient-reported questionnaires and lung function tests (LFTs) were analyzed. Increased production of interleukin (IL)-1β (p<0.001) and IL-6 (p<0.001) was found in post-COVID-19 patients from both study periods. Anti-inflammatory Th2 responses and Th17 responses were attenuated compared to controls. PACS was present in 22%: fatigue was associated with predominance of Th2 responses; abnormal LFTs with overproduction of IL-1β and IL-6. Epigenetic markers of chromatin accessibility such as H3K27Ac were associated with these changes. Importantly, anti-IL-1 treatment with anakinra during the acute phase of disease reduced the chance of developing PACS by 40%.Funding Information: The study was sponsored and funded by the Hellenic Institute for the Study of Sepsis (HISS), which was also responsible for the design, conduct, analysis and interpretation of data and the decision to publish.Declaration of Interests: E. J. Giamarellos-Bourboulis has received honoraria from Abbott CH, bioMérieux, Brahms GmbH, GSK, InflaRx GmbH, Sobi and XBiotech Inc; independent educational grants from Abbott CH, AbbVie, bioMérieux Inc, InflaRx GmbH, Johnson & Johnson, MSD, Novartis, Sobi, UCB and XBiotech Inc.; and funding from the Horizon2020 Marie-Curie Project European Sepsis Academy (granted to the National and Kapodistrian University of Athens), the Horizon 2020 European Grants ImmunoSep and RISKinCOVID (granted to the Hellenic Institute for the Study of Sepsis) and from the Horizon Europe project EPIC-CROWN-2 (granted to the Hellenic Institute for the Study of Sepsis). G. Poulakou has received independent educational grants from Pfizer, MSD, Angelini, and Biorad. H. Milionis reports receiving honoraria, consulting fees and non-financial support from healthcare companies, including Amgen, Angelini, Bayer, Mylan, MSD, Pfizer, and Servier. M. G. Netea is supported by an ERC Advanced Grant (#833247) and a Spinoza grant of the Netherlands Organization for Scientific Research. He has also received independent educational grants from TTxD, GSK and ViiV HealthCare. P. Panagopoulos has received honoraria from GILEAD Sciences, Janssen, and MSD. G. N. Dalekos is an advisor or lecturer for Ipsen, Pfizer, Genkyotex, Novartis, Sobi, received research grants from Abbvie, Gilead and has served as PI in studies for Abbvie, Novartis, Gilead, Novo Nordisk, Genkyotex, Regulus Therapeutics Inc, Tiziana Life Sciences, Bayer, Astellas, Pfizer, Amyndas Pharmaceuticals, CymaBay Therapeutics Inc., Sobi and Intercept Pharmaceuticals. S. Foutadakis and G. Vatsellas were supported by a grant to DT for the General Secreteriat for Research and Innovation (Emblematic Action on COVID-19). E. Giannitsioti has received honoraria from Pfizer Hellas, Norma Hellas and from Advisory Board in bioMerieux France. The other authors do not have any competing interest to declare.Ethics Approval Statement: The protocol was approved by the Ethics Committee of the participating hospitals (Attikon University Hospital 1-11/1/2022 and General Hospital of Piraeus Tzaneio 16-14/5/2021). All patients or their legal representatives provided written informed consent before enrollment.

The innate immune system is able to build memory-like features in response to certain infections or vaccines, resulting in enhanced responsiveness upon (re)challenge with the same or an unrelated pathogen, a phenomenon termed 'trained immunity'. Compared with antigen-dependent adaptive immune responses triggered by classical vaccines against specific pathogens, trained immunity-related vaccines induce enhanced innate immune responses against unrelated pathogens and provide 'heterologous protection'. Here, we discuss the heterologous effects of vaccines against infections and detail the latest insights into the cellular and molecular mechanisms mediating trained immunity. Additionally, novel vaccine strategies are suggested for fighting new pandemics in the future by taking advantage of the heterologous memory features of trained immunity.

Histamine-induced vascular leakage is a core process of allergic pathologies, including anaphylaxis. Here, we show that glycolysis is integral to histamine-induced endothelial barrier disruption and hyperpermeability. Histamine rapidly enhanced glycolysis in endothelial cells via a pathway that involved histamine receptor 1 and phospholipase C beta signaling. Consistently, partial inhibition of glycolysis with 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO) prevented histamine-induced hyperpermeability in human microvascular endothelial cells, by abolishing the histamine-induced actomyosin contraction, focal adherens junction formation, and endothelial barrier disruption. Pharmacologic blockade of glycolysis with 3PO in mice reduced histamine-induced vascular hyperpermeability, prevented vascular leakage in passive cutaneous anaphylaxis and protected from systemic anaphylaxis. In conclusion, we elucidated the role of glycolysis in histamine-induced disruption of endothelial barrier integrity. Our data thereby point to endothelial glycolysis as a novel therapeutic target for human pathologies related to excessive vascular leakage, such as systemic anaphylaxis.