Zhixuan Loh

Receptor for advanced glycation end products and its ligand high-mobility group box-1 mediate allergic airway sensitization and airway inflammation

BACKGROUND The receptor for advanced glycation end products (RAGE) shares common ligands and signaling pathways with TLR4, a key mediator of house dust mite (Dermatophagoides pteronyssinus) (HDM) sensitization. We hypothesized that RAGE and its ligand high-mobility group box-1 (HMGB1) cooperate with TLR4 to mediate HDM sensitization. OBJECTIVES To determine the requirement for HMGB1 and RAGE, and their relationship with TLR4, in airway sensitization. METHODS TLR4(-/-), RAGE(-/-), and RAGE-TLR4(-/-) mice were intranasally exposed to HDM or cockroach (Blatella germanica) extracts, and features of allergic inflammation were measured during the sensitization or challenge phase. Anti-HMGB1 antibody and the IL-1 receptor antagonist Anakinra were used to inhibit HMGB1 and the IL-1 receptor, respectively. RESULTS The magnitude of allergic airway inflammation in response to either HDM or cockroach sensitization and/or challenge was significantly reduced in the absence of RAGE but not further diminished in the absence of both RAGE and TLR4. HDM sensitization induced the release of HMGB1 from the airway epithelium in a biphasic manner, which corresponded to the sequential activation of TLR4 then RAGE. Release of HMGB1 in response to cockroach sensitization also was RAGE dependent. Significantly, HMGB1 release occurred downstream of TLR4-induced IL-1α, and upstream of IL-25 and IL-33 production. Adoptive transfer of HDM-pulsed RAGE(+/+)dendritic cells to RAGE(-/-) mice recapitulated the allergic responses after HDM challenge. Immunoneutralization of HMGB1 attenuated HDM-induced allergic airway inflammation. CONCLUSION The HMGB1-RAGE axis mediates allergic airway sensitization and airway inflammation. Activation of this axis in response to different allergens acts to amplify the allergic inflammatory response, which exposes it as an attractive target for therapeutic intervention.

Plasmacytoid Dendritic Cells Promote Host Defense against Acute Pneumovirus Infection via the TLR7–MyD88-Dependent Signaling Pathway

Human respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infection in infants. In human infants, plasmacytoid dendritic cells (pDC) are recruited to the nasal compartment during infection and initiate host defense through the secretion of type I IFN, IL-12, and IL-6. However, RSV-infected pDC are refractory to TLR7-mediated activation. In this study, we used the rodent-specific pathogen, pneumonia virus of mice (PVM), to determine the contribution of pDC and TLR7 signaling to the development of the innate inflammatory and early adaptive immune response. In wild-type, but not TLR7- or MyD88-deficient mice, PVM inoculation led to a marked infiltration of pDC and increased expression of type I, II, and III IFNs. The delayed induction of IFNs in the absence of TLR7 or MyD88 was associated with a diminished innate inflammatory response and augmented virus recovery from lung tissue. In the absence of TLR7, PVM-specific CD8+ T cell cytokine production was abrogated. The adoptive transfer of TLR7-sufficient, but not TLR7-deficient pDC to TLR7 gene-deleted mice recapitulated the antiviral responses observed in wild-type mice and promoted virus clearance. In summary, TLR7-mediated signaling by pDC is required for appropriate innate responses to acute pneumovirus infection. It is conceivable that as-yet–unidentified defects in the TLR7 signaling pathway may be associated with elevated levels of RSV-associated morbidity and mortality among otherwise healthy human infants.

Toll-like receptor 7 gene deficiency and early-life Pneumovirus infection interact to predispose toward the development of asthma-like pathology in mice

BACKGROUND Respiratory tract viruses are a major environmental risk factor for both the inception and exacerbations of asthma. Genetic defects in Toll-like receptor (TLR) 7-mediated signaling, impaired type I interferon responses, or both have been reported in asthmatic patients, although their contribution to the onset and exacerbation of asthma remains poorly understood. OBJECTIVE We sought to determine whether Pneumovirus infection in the absence of TLR7 predisposes to bronchiolitis and the inception of asthma. METHODS Wild-type and TLR7-deficient (TLR7(-/-)) mice were inoculated with the rodent-specific pathogen pneumonia virus of mice at 1 (primary), 7 (secondary), and 13 (tertiary) weeks of age, and pathologic features of bronchiolitis or asthma were assessed. In some experiments infected mice were exposed to low-dose cockroach antigen. RESULTS TLR7 deficiency increased viral load in the airway epithelium, which became sloughed and necrotic, and promoted an IFN-α/β(low), IL-12p70(low), IL-1β(high), IL-25(high), and IL-33(high) cytokine microenvironment that was associated with the recruitment of type 2 innate lymphoid cells/nuocytes and increased TH2-type cytokine production. Viral challenge of TLR7(-/-) mice induced all of the cardinal pathophysiologic features of asthma, including tissue eosinophilia, mast cell hyperplasia, IgE production, airway smooth muscle alterations, and airways hyperreactivity in a memory CD4(+) T cell-dependent manner. Importantly, infections with pneumonia virus of mice promoted allergic sensitization to inhaled cockroach antigen in the absence but not the presence of TLR7. CONCLUSION TLR7 gene defects and Pneumovirus infection interact to establish an aberrant adaptive response that might underlie virus-induced asthma exacerbations in later life.

The plasmacytoid dendritic cell: at the cross-roads in asthma

The onset, progression and exacerbations of asthma are frequently associated with viral infections of the lower respiratory tract. An emerging paradigm suggests that this relationship may be underpinned by a defect in the host’s antiviral response, typified by the impaired production of type I and type III interferons (IFNs). The failure to control viral burden probably causes damage to the lung architecture and contributes to an aberrant immune response, which together compromise lung function. Although a relatively rare cell type, the plasmacytoid dendritic cell dedicates much of its transcriptome to the synthesis of IFNs and is pre-armed with virus-sensing pattern recognition receptors. Thus, plasmacytoid dendritic cells are specialised to ensure early viral detection and the rapid induction of the antiviral state to block viral replication and spread. In addition, plasmacytoid dendritic cells can limit immunopathology, and promote peripheral tolerance to prevent allergic sensitisation to harmless antigens, possibly through the induction of regulatory T-cells. Thus, this enigmatic cell may lie at an important intersection, orchestrating the immediate phase of antiviral immunity to effect viral clearance while regulating tolerance. Here, we review the evidence to support the hypothesis that a primary defect in plasmacytoid dendritic function may underlie the development of asthma. A review of the evidence on the role of plasmacytoid dendritic function in the development of asthma http://ow.ly/qieyN

Allergen-induced IL-6 trans-signaling activates γδ T cells to promote type 2 and type 17 airway inflammation

BACKGROUND A variant in the IL-6 receptor (IL-6R) gene increases asthma risk and is predicted to decrease IL-6 classic signaling and increase IL-6 trans-signaling. This suggests that inhibition of IL-6 trans-signaling, but not classic signaling, might suppress allergic airway inflammation. OBJECTIVES We sought to determine whether IL-6 signaling contributes to (1) acute experimental asthma induced by clinically relevant allergens and (2) variation in asthma clinical phenotypes in asthmatic patients. METHODS Mice were sensitized to house dust mite (HDM) or cockroach at day 0, treated with IL-6R inhibitors at day 13, and challenged with the same allergen at days 14 to 17. End points were measured 3 hours after the final challenge. IL-6 and soluble IL-6 receptor (sIL-6R) expression in induced sputum of asthmatic patients was correlated with asthma clinical phenotypes. RESULTS Both HDM and cockroach induced a type 2/type 17 cytokine profile and mixed granulocytic inflammation in the airways. Both allergens increased IL-6 expression in the airways, but only cockroach induced sIL-6R expression. Therefore HDM challenge promoted IL-6 classic signaling but not trans-signaling; in this model treatment with anti-IL-6R did not suppress airway inflammation. In contrast, cockroach-induced inflammation involved activation of IL-6 trans-signaling and production of IL-17A by γδ T cells. Anti-IL-6R, selective blockade of sIL-6R, or γδ T-cell deficiency significantly attenuated cockroach-induced inflammation. Asthmatic patients with high airway IL-6 and sIL-6R levels were enriched for the neutrophilic and mixed granulocytic subtypes. CONCLUSION Experimental asthma associated with both high IL-6 and high sIL-6R levels in the airways is attenuated by treatment with IL-6R inhibitors.

Absence of Toll–IL-1 Receptor 8/Single Immunoglobulin IL-1 Receptor–Related Molecule Reduces House Dust Mite–Induced Allergic Airway Inflammation in Mice

Allergic asthma is a chronic inflammatory disease predominately associated with the activation of CD4(+) T helper Type 2 (Th2) cells. Innate pattern recognition receptors are widely acknowledged to shape the adaptive immune response. For example, the activation of airway epithelial Toll-like receptor-4 (TLR4) is necessary for the generation of house dust mite (HDM)-specific Th2 responses and the development of asthma in mice. Here we sought to determine whether the absence of Toll-interleukin-1 receptor (TIR)-8, a negative regulator of TLR4 signaling that is highly expressed in airway epithelial cells, would exacerbate HDM-induced asthma in a murine model. We found that Th2 but not Th1 or Th17 cytokine expression was significantly reduced in the lung and draining lymph nodes in HDM-sensitized/challenged TIR8 gene-deleted mice. Mucus-producing goblet cells, HDM-specific IgG1, and airway hyperreactivity were also significantly reduced in HDM-exposed, TIR8-deficient mice. Consistent with the attenuated Th2 response, eotaxin-2/CCL24 expression and airway and peribronchial eosinophils were significantly reduced in the absence of TIR8. In contrast, IL-17A-responsive chemokines and neutrophil numbers were unaffected. Similar findings were obtained for cockroach allergen. HDM sensitization alone up-regulated the expression of IL-1F5, a putative TIR8 ligand and inducer of IL-4. Of note, innate IL-4, IL-5, IL-13, and IL-33 cytokine expression was reduced during HDM sensitization in the absence of TIR8, as was the recruitment of conventional dendritic cells and basophils to the draining lymph nodes. Our findings suggest that TIR8 enhances the development of HDM-induced innate and adaptive Th2, but not Th1 or Th17 type immunity.

RAGE deficiency predisposes mice to virus-induced paucigranulocytic asthma

Asthma is a chronic inflammatory disease. Although many patients with asthma develop type-2 dominated eosinophilic inflammation, a number of individuals develop paucigranulocytic asthma, which occurs in the absence of eosinophilia or neutrophilia. The aetiology of paucigranulocytic asthma is unknown. However, both respiratory syncytial virus (RSV) infection and mutations in the receptor for advanced glycation endproducts (RAGE) are risk factors for asthma development. Here, we show that RAGE deficiency impairs anti-viral immunity during an early-life infection with pneumonia virus of mice (PVM; a murine analogue of RSV). The elevated viral load was associated with the release of high mobility group box-1 (HMGB1) which triggered airway smooth muscle remodelling in early-life. Re-infection with PVM in later-life induced many of the cardinal features of asthma in the absence of eosinophilic or neutrophilic inflammation. Anti-HMGB1 mitigated both early-life viral disease and asthma-like features, highlighting HMGB1 as a possible novel therapeutic target. DOI: http://dx.doi.org/10.7554/eLife.21199.001

Exploiting a novel conformational switch to control innate immunity mediated by complement protein C3a

Complement C3a is an important protein in innate and adaptive immunity, but its specific roles in vivo remain uncertain because C3a degrades rapidly to form the C3a-desArg protein, which does not bind to the C3a receptor and is indistinguishable from C3a using antibodies. Here we develop the most potent, stable and highly selective small molecule modulators of C3a receptor, using a heterocyclic hinge to switch between agonist and antagonist ligand conformations. This enables characterization of C3 areceptor-selective pro- vs. anti-inflammatory actions in human mast cells and macrophages, and in rats. A C3a receptor-selective agonist induces acute rat paw inflammation by first degranulating mast cells before activating macrophages and neutrophils. An orally administered C3a receptor-selective antagonist inhibits mast cell degranulation, thereby blocking recruitment and activation of macrophages and neutrophils, expression of inflammatory mediators and inflammation in a rat paw edema model. These novel tools reveal the mechanism of C3a-induced inflammation and provide new insights to complement-based medicines.Complement C3a is an important protein in innate and adaptive immunity, but its roles in vivo are unclear. Here the authors develop novel chemical agonists and antagonists for the C3a receptor, and show that they modulate mast cell degranulation and inflammation in a rat paw edema model

Plasmacytoid dendritic cells protect from viral bronchiolitis and asthma through semaphorin 4a-mediated T reg expansion

Respiratory syncytial virus–bronchiolitis is a major independent risk factor for subsequent asthma, but the causal mechanisms remain obscure. We identified that transient plasmacytoid dendritic cell (pDC) depletion during primary Pneumovirus infection alone predisposed to severe bronchiolitis in early life and subsequent asthma in later life after reinfection. pDC depletion ablated interferon production and increased viral load; however, the heightened immunopathology and susceptibility to subsequent asthma stemmed from a failure to expand functional neuropilin-1+ regulatory T (T reg) cells in the absence of pDC-derived semaphorin 4a (Sema4a). In adult mice, pDC depletion predisposed to severe bronchiolitis only after antibiotic treatment. Consistent with a protective role for the microbiome, treatment of pDC-depleted neonates with the microbial-derived metabolite propionate promoted Sema4a-dependent T reg cell expansion, ameliorating both diseases. In children with viral bronchiolitis, nasal propionate levels were decreased and correlated with an IL-6high/IL-10low microenvironment. We highlight a common but age-related Sema4a-mediated pathway by which pDCs and microbial colonization induce T reg cell expansion to protect against severe bronchiolitis and subsequent asthma.

Hepatic expression profiling identifies steatosis-independent and steatosis-driven advanced fibrosis genes

Chronic liver disease (CLD) is associated with tissue-destructive fibrosis. Considering that common mechanisms drive fibrosis across etiologies, and that steatosis is an important cofactor for pathology, we performed RNA sequencing on liver biopsies of patients with different fibrosis stages, resulting from infection with hepatitis C virus (HCV) (with or without steatosis) or fatty liver disease. In combination with enhanced liver fibrosis score correlation analysis, we reveal a common set of genes associated with advanced fibrosis, as exemplified by those encoding the transcription factor ETS-homologous factor (EHF) and the extracellular matrix protein versican (VCAN). We identified 17 fibrosis-associated genes as candidate EHF targets and demonstrated that EHF regulates multiple fibrosis-associated genes, including VCAN, in hepatic stellate cells. Serum VCAN levels were also elevated in advanced fibrosis patients. Comparing biopsies from patients with HCV with or without steatosis, we identified a steatosis-enriched gene set associated with advanced fibrosis, validating follistatin-like protein 1 (FSTL1) as an exemplar of this profile. In patients with advanced fibrosis, serum FSTL1 levels were elevated in those with steatosis (versus those without). Liver Fstl1 mRNA levels were also elevated in murine CLD models. We thus reveal a common gene signature for CLD-associated liver fibrosis and potential biomarkers and/or targets for steatosis-associated liver fibrosis.