Indoleamine 2,3-dioxygenase (IDO)-1 and IDO-2 activity and severe course of COVID-19.

COVID-19 is a pandemic with high morbidity and mortality. In an autopsy cohort of COVID-19 patients, we found extensive accumulation of the tryptophan degradation products 3-hydroxy-anthranilic acid and quinolinic acid in the lungs, heart, and brain. This was not related to the expression of the tryptophan-catabolizing indoleamine 2,3-dioxygenase (IDO)-1, but rather to that of its isoform IDO-2, which otherwise is expressed rarely. Bioavailability of tryptophan is an absolute requirement for proper cell functioning and synthesis of hormones, whereas its degradation products can cause cell death. Markers of apoptosis and severe cellular stress were associated with IDO-2 expression in large areas of lung and heart tissue, whereas affected areas in brain were more restricted. Analyses of tissue, cerebrospinal fluid, and sequential plasma samples indicate early initiation of the kynurenine/aryl-hydrocarbon receptor/IDO-2 axis as a positive feedback loop, potentially leading to severe COVID-19 pathology. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Metabolic differences between bronchial epithelium from healthy individuals and patients with asthma and the effect of bronchial thermoplasty.

BACKGROUND: Asthma is a heterogeneous disease with differences in onset, severity, and inflammation. Bronchial epithelial cells (BECs) contribute to asthma pathophysiology. OBJECTIVE: We determined whether transcriptomes of BECs reflect heterogeneity in inflammation and severity in asthma, and whether this was affected in BECs from patients with severe asthma after their regeneration by bronchial thermoplasty. METHODS: RNA sequencing was performed on BECs obtained by bronchoscopy from healthy controls (n = 16), patients with mild asthma (n = 17), patients with moderate asthma (n = 5), and patients with severe asthma (n = 17), as well as on BECs from treated and untreated airways of the latter (also 6 months after bronchial thermoplasty) (n = 23). Lipidome and metabolome analyses were performed on cultured BECs from healthy controls (n = 7); patients with severe asthma (n = 9); and, for comparison, patients with chronic obstructive pulmonary disease (n = 7). RESULTS: Transcriptome analysis of BECs from patients showed a reduced expression of oxidative phosphorylation (OXPHOS) genes, most profoundly in patients with severe asthma but less profoundly and more heterogeneously in patients with mild asthma. Genes related to fatty acid metabolism were significantly upregulated in asthma. Lipidomics revealed enhanced levels of lipid species (phosphatidylcholines, lysophosphatidylcholines. and bis(monoacylglycerol)phosphate), whereas levels of OXPHOS metabolites were reduced in BECs from patients with severe asthma. BECs from patients with mild asthma characterized by hyperresponsive production of mediators implicated in neutrophilic inflammation had decreased expression of OXPHOS genes compared with that in BECs from patients with mild asthma with normoresponsive production. BECs obtained after thermoplasty had significantly increased expression of OXPHOS genes and decreased expression of fatty acid metabolism genes compared with BECs obtained from untreated airways. CONCLUSION: BECs in patients with asthma are metabolically different from those in healthy individuals. These differences are linked with inflammation and asthma severity, and they can be reversed by bronchial thermoplasty.

Anti-IL-5 in Mild Asthma Alters Rhinovirus-induced Macrophage, B-Cell, and Neutrophil Responses (MATERIAL). A Placebo-controlled, Double-Blind Study.

RATIONALE: Eosinophils drive pathophysiology in stable and exacerbating eosinophilic asthma, and therefore treatment is focused on the reduction of eosinophil numbers. Mepolizumab, a humanized monoclonal antibody that neutralizes IL-5 and efficiently attenuates eosinophils, proved clinically effective in severe eosinophilic asthma but not in mild asthma. OBJECTIVES: To study the effect of mepolizumab on virus-induced immune responses in mild asthma. METHODS: Patients with mild asthma, steroid-naive and randomized for eosinophil numbers, received 750 mg mepolizumab intravenously in a placebo-controlled double-blind trial, 2 weeks after which patients were challenged with rhinovirus (RV) 16. FEV1, FVC, fractional exhaled nitric oxide, symptom scores (asthma control score), viral load (PCR), eosinophil numbers, humoral (luminex, ELISA), and cellular (flow cytometry) immune parameters in blood, BAL fluid, and sputum, before and after mepolizumab and RV16, were assessed. MEASUREMENTS AND MAIN RESULTS: Mepolizumab attenuated baseline blood eosinophils and their activation, attenuated trendwise sputum eosinophils, and enhanced circulating natural killer cells. Mepolizumab did not affect FEV1, FVC, and fractional exhaled nitric oxide, neither at baseline nor after RV16. On RV16 challenge mepolizumab did not prevent eosinophil activation but did enhance local B lymphocytes and macrophages and reduce neutrophils and their activation. Mepolizumab also enhanced secretory IgA and reduced tryptase in BAL fluid. Finally, mepolizumab affected particularly RV16-induced macrophage inflammatory protein-3a, vascular endothelial growth factor-A, and IL-1RA production in BAL fluid. CONCLUSIONS: Mepolizumab failed to prevent activation of remaining eosinophils and changed RV16-induced immune responses in mild asthma. Although these latter effects likely are caused by attenuated eosinophil numbers, we cannot exclude a role for basophils. Clinical trial registered with www.clinicaltrials.gov (NCT 01520051).

IL-33 drives influenza-induced asthma exacerbations by halting innate and adaptive antiviral immunity.

BACKGROUND: Influenza virus triggers severe asthma exacerbations for which no adequate treatment is available. It is known that IL-33 levels correlate with exacerbation severity, but its role in the immunopathogenesis of exacerbations has remained elusive. OBJECTIVE: We hypothesized that IL-33 is necessary to drive asthma exacerbations. We intervened with the IL-33 cascade and sought to dissect its role, also in synergy with thymic stromal lymphopoietin (TSLP), in airway inflammation, antiviral activity, and lung function. We aimed to unveil the major source of IL-33 in the airways and IL-33-dependent mechanisms that underlie severe asthma exacerbations. METHODS: Patients with mild asthma were experimentally infected with rhinovirus. Mice were chronically exposed to house dust mite extract and then infected with influenza to resemble key features of exacerbations in human subjects. Interventions included the anti-IL-33 receptor ST2, anti-TSLP, or both. RESULTS: We identified bronchial ciliated cells and type II alveolar cells as a major local source of IL-33 during virus-driven exacerbation in human subjects and mice, respectively. By blocking ST2, we demonstrated that IL-33 and not TSLP was necessary to drive exacerbations. IL-33 enhanced airway hyperresponsiveness and airway inflammation by suppressing innate and adaptive antiviral responses and by instructing epithelial cells and dendritic cells of house dust mite-sensitized mice to dampen IFN-ß expression and prevent the TH1-promoting dendritic cell phenotype. IL-33 also boosted luminal NETosis and halted cytolytic antiviral activities but did not affect the TH2 response. CONCLUSION: Interventions targeting the IL-33/ST2 axis could prove an effective acute short-term therapy for virus-induced asthma exacerbations.

Neutrophilic inflammation in asthma and defective epithelial translational control.

Neutrophilic inflammation in asthma is associated with interleukin (IL)-17A, corticosteroid-insensitivity and bronchodilator-induced forced expiratory volume in 1 s (FEV1) reversibility. IL-17A synergises with tumour necrosis factor (TNF)-α in the production of the neutrophil chemokine CXCL-8 by primary bronchial epithelial cells (PBECs).We hypothesised that local neutrophilic inflammation in asthma correlates with IL-17A and TNF-α-induced CXCL-8 production by PBECs from asthma patients.PBECs from most asthma patients displayed an exaggerated CXCL-8 production in response to TNF-α and IL-17A, but not to TNF-α alone, and which was also insensitive to corticosteroids. This hyperresponsiveness of PBECs strongly correlated with CXCL-8 levels and neutrophil numbers in bronchoalveolar lavage from the corresponding patients, but not with that of eosinophils. In addition, this hyperresponsiveness also correlated with bronchodilator-induced FEV1 % reversibility. At the molecular level, epithelial hyperresponsiveness was associated with failure of the translational repressor T-cell internal antigen-1 related protein (TiAR) to translocate to the cytoplasm to halt CXCL-8 production, as confirmed by TiAR knockdown. This is in line with the finding that hyperresponsive PBECs also produced enhanced levels of other inflammatory mediators.Hyperresponsive PBECs in asthma patients may underlie neutrophilic and corticosteroid-insensitive inflammation and a reduced FEV1, irrespective of eosinophilic inflammation. Normalising cytoplasmic translocation of TiAR is a potential therapeutic target in neutrophilic, corticosteroid-insensitive asthma.

Eosinophils capture viruses, a capacity that is defective in asthma.

BACKGROUND: Activated eosinophils cause major pathology in stable and exacerbating asthma; however, they can also display protective properties like an extracellular antiviral activity. Initial murine studies led us to further explore a potential intracellular antiviral activity by eosinophils. METHODS: To follow eosinophil-virus interaction, respiratory syncytial virus (RSV) and influenza virus were labeled with a fluorescent lipophilic dye (DiD). Interactions with eosinophils were visualized by confocal microscopy, electron microscopy, and flow cytometry. Eosinophil activation was assessed by both flow cytometry and ELISA. In a separate study, eosinophils were depleted in asthma patients using anti-IL-5 (mepolizumab), followed by a challenge with rhinovirus-16 (RV16). RESULTS: DiD-RSV and DiD-influenza rapidly adhered to human eosinophils and were internalized and inactivated (95% in ≤ 2 hours) as reflected by a reduced replication in epithelial cells. The capacity of eosinophils to capture virus was reduced up to 75% with increasing severity of asthma. Eosinophils were activated by virus in vitro and in vivo. In vivo this correlated with virus-induced loss of asthma control. CONCLUSIONS: This previously unrecognized and in asthma attenuated antiviral property provides a new perspective to eosinophils in asthma. This is indicative of an imbalance between protective and cytotoxic properties by eosinophils that may underlie asthma exacerbations.

IL-17 attenuates degradation of ARE-mRNAs by changing the cooperation between AU-binding proteins and microRNA16.

Interleukin 17A (IL-17), a mediator implicated in chronic and severe inflammatory diseases, enhances the production of pro-inflammatory mediators by attenuating decay of the encoding mRNAs. The decay of many of these mRNAs depends on proteins (AUBps) that target AU-rich elements in the 3'-untranslated region of mRNAs and facilitate either mRNA decay or stabilization. Here we show that AUBps and the target mRNA assemble in a novel ribonucleoprotein complex in the presence of microRNA16 (miR16), which leads to the degradation of the target mRNA. Notably, IL-17 attenuates miR16 expression and promotes the binding of stabilizing AUBps over that of destabilizing AUBps, reducing mRNA decay. These findings indicate that miR16 independently of a seed sequence, directs the competition between degrading and stabilizing AUBps for target mRNAs. Since AUBps affect expression of about 8% of the human transcriptome and miR16 is ubiquitously expressed, IL-17 may in addition to inflammation affect many other cellular processes.

Systemic tryptophan and kynurenine catabolite levels relate to severity of rhinovirus-induced asthma exacerbation: a prospective study with a parallel-group design.

BACKGROUND: Patients with allergic asthma have exacerbations which are frequently caused by rhinovirus infection. The antiviral tryptophan-catabolising enzyme indoleamine 2,3-dioxygenase (IDO) is induced by interferon-γ and suppressed by Th2 mediators interleukin (IL)-4 and IL-13. We hypothesised that local IDO activity after viral airway infection is lower in patients with allergic asthma than in healthy controls. OBJECTIVE: To determine whether IDO activity differs between patients with allergic asthma and healthy individuals before and after rhinovirus infection. METHODS: Healthy individuals and patients with allergic asthma were experimentally infected with low-dose (10 TCID50) rhinovirus 16. Blood, bronchoalveolar lavage fluid and exhaled breath condensate (for mass spectrometry by UPLC-MS/MS) were obtained before and after rhinovirus challenge. RESULTS: IDO activity was not induced by rhinovirus infection in either group, despite increases in cold scores. However, baseline pulmonary IDO activity was lower in patients with allergic asthma than in healthy individuals. In contrast, systemic tryptophan and its catabolites were markedly higher in patients with allergic asthma. Moreover, systemic quinolinic acid and tryptophan were associated with eosinophil cationic protein (r=0.43 and r=0.78, respectively) and eosinophils (r=0.38 and r=0.58, respectively) in bronchoalveolar lavage fluid and peak asthma symptom scores after rhinovirus challenge (r=0.53 and r=0.64, respectively). CONCLUSIONS: Rhinovirus infection by itself induces no IDO activity, but the reduced pulmonary IDO activity in patients with allergic asthma at baseline may underlie a reduced control of viral infections. Notably, the enhanced systemic catabolism of tryptophan in patients with allergic asthma was strongly related to the outcome of rhinovirus challenge in asthma and may serve as a prognostic factor.

Transcriptome sequencing (RNA-Seq) of human endobronchial biopsies: asthma versus controls.

The cellular and molecular pathways in asthma are highly complex. Increased understanding can be obtained by unbiased transcriptomic analysis (RNA-Seq). We hypothesised that the transcriptomic profile of whole human endobronchial biopsies differs between asthma patients and controls. First, we investigated the feasibility of obtaining RNA from whole endobronchial biopsies suitable for RNA-Seq. Secondly, we examined the difference in transcriptomic profiles between asthma and controls. This cross-sectional study compared four steroid-free atopic asthma patients and five healthy nonatopic controls. Total RNA from four biopsies per subject was prepared for RNA-Seq. Comparison of the numbers of reads per gene in asthma and controls was based on the Poisson distribution. 46 genes were differentially expressed between asthma and controls, including pendrin, periostin and BCL2. 10 gene networks were found to be involved in cellular morphology, movement and development. RNA isolated from whole human endobronchial biopsies is suitable for RNA-Seq, showing different transcriptomic profiles between asthma and controls. Novel and confirmative genes were found to be linked to asthma. These results indicate that biological processes in the airways of asthma patients are regulated differently when compared to controls, which may be relevant for the pathogenesis and treatment of the disease.

Prolonged indoleamine 2,3-dioxygenase-2 activity and associated cellular stress in post-acute sequelae of SARS-CoV-2 infection.

BACKGROUND: Post-acute sequela of SARS-CoV-2 infection (PASC) encompass fatigue, post-exertional malaise and cognitive problems. The abundant expression of the tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase-2 (IDO2) in fatal/severe COVID-19, led us to determine, in an exploratory observational study, whether IDO2 is expressed and active in PASC, and may correlate with pathophysiology. METHODS: Plasma or serum, and peripheral blood mononuclear cells (PBMC) were obtained from well-characterized PASC patients and SARS-CoV-2-infected individuals without PASC. We assessed tryptophan and its degradation products by UPLC-MS/MS. IDO2 activity, its potential consequences, and the involvement of the aryl hydrocarbon receptor (AHR) in IDO2 expression were determined in PBMC from another PASC cohort by immunohistochemistry (IHC) for IDO2, IDO1, AHR, kynurenine metabolites, autophagy, and apoptosis. These PBMC were also analyzed by metabolomics and for mitochondrial functioning by respirometry. IHC was also performed on autopsy brain material from two PASC patients. FINDINGS: IDO2 is expressed and active in PBMC from PASC patients, as well as in brain tissue, long after SARS-CoV-2 infection. This is paralleled by autophagy, and in blood cells by reduced mitochondrial functioning, reduced intracellular levels of amino acids and Krebs cycle-related compounds. IDO2 expression and activity is triggered by SARS-CoV-2-infection, but the severity of SARS-CoV-2-induced pathology appears related to the generated specific kynurenine metabolites. Ex vivo, IDO2 expression and autophagy can be halted by an AHR antagonist. INTERPRETATION: SARS-CoV-2 infection triggers long-lasting IDO2 expression, which can be halted by an AHR antagonist. The specific kynurenine catabolites may relate to SARS-CoV-2-induced symptoms and pathology. FUNDING: None.

Imprinting of bronchial epithelial cells upon in vivo rhinovirus infection in people with asthma.

Background: Defective translocation of the translational repressor TIAR (T-cell internal antigen receptor) in bronchial epithelial cells (BECs) from asthma patients underlies epithelial hyperresponsiveness, reflected by an exaggerated production of a select panel of inflammatory cytokines such as CXCL-8, interleukin (IL)-6, granulocyte colony-stimulating factor, CXCL-10, upon exposure to tumour necrosis factor (TNF) and IL-17A. With this study we aimed to clarify whether epithelial hyperresponsiveness is a consistent finding, is changed upon in vivo exposure to rhinovirus (RV)-A16 and applies to the bronchoconstrictor endothelin-1. Methods: BECs were obtained from asthma patients (n=18) and healthy individuals (n=11), 1 day before and 6 days post-RV-A16 exposure. BECs were cultured and stimulated with TNF and IL-17A and inflammatory mediators were analysed. The bronchoalveolar lavage fluid (BALF) was obtained in parallel with BECs to correlate differential cell counts and inflammatory mediators with epithelial hyperresponsiveness. Results: Epithelial hyperresponsiveness was confirmed in sequential samples and even increased in BECs from asthma patients after RV-A16 exposure, but not in BECs from healthy individuals. Endothelin-1 tended to increase in BECs from asthma patients collected after RV-A16 exposure, but not in BECs from healthy individuals. In vitro CXCL-8 and endothelin-1 production correlated. In vivo relevance for in vitro CXCL-8 and endothelin-1 production was shown by correlations with forced expiratory volume in 1 s % predicted and CXCL-8 BALF levels. Conclusion: Epithelial hyperresponsiveness is an intrinsic defect in BECs from asthma patients, which increases upon viral exposure, but not in BECs from healthy individuals. This epithelial hyperresponsiveness also applies to the bronchoconstrictor endothelin-1, which could be involved in airway obstruction.

Leukemia-specific T-cell reactivity induced by leukemic dendritic cells is augmented by 4-1BB targeting.

PURPOSE: Acute myelogenous leukemia (AML) blasts are able to differentiate into leukemia-derived dendritic cells (AML-DC), thereby enabling efficient presentation of known and unknown leukemic antigens. Advances in culture techniques and AML-DC characterization justify clinical application. However, additional measures are likely needed to potentiate vaccines and overcome the intrinsic tolerant state of the patients' immune system. Engagement of the costimulatory molecule 4-1BB can break immunologic tolerance and increase CTL responses. In this study, we examined the role of the 4-1BB ligand (4-1BBL) on T-cell responses induced by AML-DC. EXPERIMENTAL DESIGN: In allogeneic and autologous cocultures of T cells and AML-DC, the effect of the addition of 4-1BBL on T-cell proliferation, T-cell subpopulations, and T-cell function was determined. RESULTS: Addition of 4-1BBL to cocultures of AML-DC and T cells induced a preferential increase in the proliferation of CD8(+) T cells. Increased differentiation into effector and central memory populations was observed in both CD4(+) and CD8(+) T cells in the presence of 4-1BBL. AML-DC induce a T helper 1 response, characterized by high IFN-gamma production, which is significantly increased by targeting 4-1BB. T cells primed in the presence of 4-1BBL show specificity for the leukemia-associated antigen Wilms' tumor 1, whereas cytotoxicity assays with leukemic blast targets showed the cytolytic potential of T cells primed in the presence of 4-1BBL. CONCLUSION: We conclude that 4-1BBL is an effective adjuvant to enhance T-cell responses elicited by AML-DC.

Responses to malarial antigens are altered in helminth-infected children.

Malaria and helminth infections often coincide in the same tropical regions. Studies of the consequences of helminth and malaria coinfection in humans have been few and are mainly epidemiological, with little information on cellular immune responses. In this study, we investigated the antimalarial immune responses of Ghanaian children living in a rural area with a high prevalence of both helminth infection and Plasmodium falciparum infection. Whole blood specimens were cultured with P. falciparum-infected red blood cells (iRBCs), and pro- and anti-inflammatory cytokines and immune regulatory molecules were measured. In response to iRBCs, levels of interleukin (IL)-10, but not tumor necrosis factor-alpha,were higher in samples from helminth-infected children than in those from uninfected children, as was expression of the regulatory molecules suppressor of cytokine signaling (SOCS)-3, Foxp3, and programmed death (PD)-1. Furthermore, a significant correlation was found between SOCS-3 gene expression and IL-10 production. These results indicate that the presence of helminth infection modulates the immune response to malarial parasites, making it more anti-inflammatory.