LYSMD3: A mammalian pattern recognition receptor for chitin.

Chitin, a major component of fungal cell walls, has been associated with allergic disorders such as asthma. However, it is unclear how mammals recognize chitin and the principal receptor(s) on epithelial cells that sense chitin remain to be determined. In this study, we show that LYSMD3 is expressed on the surface of human airway epithelial cells and demonstrate that LYSMD3 is able to bind chitin, as well as ß-glucan, on the cell walls of fungi. Knockdown or knockout of LYSMD3 also sharply blunts the production of inflammatory cytokines by epithelial cells in response to chitin and fungal spores. Competitive inhibition of the LYSMD3 ectodomain by soluble LYSMD3 protein, multiple ligands, or antibody against LYSMD3 also blocks chitin signaling. Our study reveals LYSMD3 as a mammalian pattern recognition receptor (PRR) for chitin and establishes its role in epithelial cell inflammatory responses to chitin and fungi.

Development and application of novel immunoassays for eosinophil granule major basic proteins to evaluate eosinophilia and myeloproliferative disorders.

BACKGROUND: During eosinophil differentiation, the granule eosinophil major basic protein 1 (eMBP1) is synthesized as a 32-kDa precursor form, referred to as proMBP1, which is processed into the 14-kDa mature form of eMBP1. The prevalence of these two forms of MBP1 in most pathological conditions remains unknown. OBJECTIVE: To develop the immunoassays that differentiate mature eMBP1 and proMBP1 and apply them to analyze their levels in biological fluids from patients with eosinophilia and hematologic disorders. METHODS: We produced a series of monoclonal antibodies and selected pairs capable of discriminating between the two molecular forms of eMBP1. Radioimmunoassay (RIA) was performed to simultaneously quantitate the levels of mature eMBP1 and proMBP1 in secretions from patients with chronic rhinosinusitis (CRS) and sera from patients with hypereosinophilic syndrome (HES) and other myeloproliferative disorders. RESULTS: The novel immunoassays possessed less than 1% crossreactivity between mature eMBP1 and proMBP1. Mature eMBP1, but not proMBP1, was found in nasal secretions of CRS patients. In contrast, elevated serum levels of mature eMBP1 and proMBP1 were observed in approximately 60% and 90% of HES patients, respectively, with proMBP1 present in greater quantities than mature eMBP1. Patients with several myeloproliferative disorders also showed high serum levels of proMBP1 while mature eMBP1 remained at basal levels. CONCLUSION: The novel immunoassays successfully differentiated mature eMBP1 and proMBP1 in human biological fluids. Further studies addressing the clinical correlates of these assays will help to develop biomarkers to diagnose and monitor patients with eosinophilia and myeloproliferative disorders.

Fungal allergen-induced IL-33 secretion involves cholesterol-dependent, VDAC-1-mediated ATP release from the airway epithelium.

KEY POINTS: Alternaria aeroallergens induce the release of ATP from human bronchial epithelial (HBE) cells by activating a conductive pathway involving voltage-dependent anion channel-1 (VDAC-1) and by exocytosis of ATP localized within membrane vesicles. Inhibition of VDAC-1 blocked Alternaria-evoked Ca2+ uptake across the plasma membrane of HBE cells and interleukin (IL)-33 release into the extracellular media. Reducing cholesterol content with a cholesterol scavenger (ß-methylcyclodextrin) or statin compound (simvastatin) blocked ATP and IL-33 release by lowering the expression of VDAC-1 in the plasma membrane. Pretreatment with simvastatin for 24 h also inhibited the increase in tight junction macromolecule permeability that occurs following Alternaria exposure. These results establish a novel role for VDAC-1 as a mechanism underlying ATP release induced by fungal allergens and suggests a possible therapeutic use for cholesterol lowering compounds in reducing Alternaria-stimulated allergic inflammation. ABSTRACT: Human bronchial epithelial (HBE) cells exposed to allergens derived from the common saprophytic fungus, Alternaria alternata release ATP, which in turn stimulates P2X7 receptor-mediated Ca2+ uptake across the plasma membrane. The subsequent increase in intracellular calcium concentration induces proteolytic processing and secretion of interleukin (IL)-33, a critical cytokine involved in the initiation of allergic airway inflammation. A major objective of the present study was to identify the mechanism responsible for conductive ATP release. The results show that pretreatment of HBE cells with inhibitors of the voltage-dependent anion channel-1 (VDAC-1) or treatment with a VDAC-1 selective blocking antibody or silencing mRNA expression of the channel by RNA interference, inhibit Alternaria-evoked ATP release. Moreover, inhibition of VDAC-1 channel activity or reducing protein expression blocked the secretion of IL-33. Similarly, reducing the cholesterol content of HBE cells with simvastatin or the cholesterol scavenger ß-methylcyclodextrin also blocked ATP release and IL-33 secretion by decreasing the level of VDAC-1 expression in the plasma membrane. In addition, simvastatin inhibited the increase in tight junction macromolecule permeability that was previously observed after Alternaria exposure. These results demonstrate a novel function for VDAC-1 as the conductive mechanism responsible for Alternaria-induced ATP release, an essential early step in the processing, mobilization and secretion of IL-33 by the airway epithelium. Furthermore, the simvastatin-evoked reduction of VDAC-1 expression in the plasma membrane, suggests the possibility that cholesterol lowering compounds may be beneficial in alleviating allergic airway inflammation induced by fungal allergens.

Early Life Represents a Vulnerable Time Window for IL-33-Induced Peripheral Lung Pathology.

IL-33, an IL-1 family cytokine, is constitutively expressed in mucosal tissues and other organs in healthy humans and animals, and expression levels increase in inflammatory conditions. Although IL-33-mediated promotion of type 2 immune responses has been well established, a gap in our knowledge regarding the functional diversity of this pleiotropic cytokine remains. To address this gap, we developed a new IL-33 transgenic mouse model in which overexpression of full-length IL-33 is induced in lung epithelial cells under conditional control. In adult mice, an ∼3-fold increase in the steady-state IL-33 levels produced no pathologic effects in the lungs. When exposed to airborne allergens, adult transgenic mice released more IL-33 extracellularly and exhibited robust type 2 immune responses. In neonatal transgenic mice, up to postnatal day 14, a similar increase in steady-state IL-33 levels resulted in increased mortality, enlarged alveolar spaces resembling bronchopulmonary dysplasia, and altered expression of genes associated with tissue morphogenesis. Processed 25-kDa IL-33 protein was detected in bronchoalveolar lavage fluids without any exogenous stimuli, and pathologic changes were abolished in mice deficient in the IL-33 receptor ST2. These findings suggest that adult lungs are relatively resistant to IL-33 overexpression unless they encounter environmental insults, whereas developing lungs are highly susceptible, with IL-33 overexpression resulting in detrimental and pathologic outcomes.

Unsupervised network mapping of commercially available immunoassay yields three distinct chronic rhinosinusitis endotypes.

BACKGROUND: Endotyping chronic rhinosinusitis (CRS) through simplified cytokine assays may help direct individualized therapy such as corticosteroids, antibiotics, or biologics. We performed an unsupervised network analysis to endotype CRS and control subjects using a commercially available cytokine-chemokine immunoassay. METHODS: A 41-plex cytokine-chemokine array along with major basic protein (MBP) assay was performed on sinonasal surgical tissue of 32 adults. Subjects were defined as non-CRS controls (n = 6), CRS with nasal polyps (CRSwNP; n = 13), and CRS without nasal polyps (CRSsNP; n = 13). Unsupervised network modeling was performed to reveal association cytokine-chemokine ("analyte") clusters and "subject" groups. RESULTS: Network mapping and unsupervised clustering revealed 3 analyte clusters and 3 subject groups. Analyte cluster-1 was composed of T helper 1 (Th1)/Th17 type markers, analyte cluster-2 Th2 markers, and analyte cluster-3 chemokines (CC) and growth factors (GF). Subject group-1 was devoid of CRSwNP, had fewer asthmatics, and was associated most strongly with analyte cluster-3 (CC/GF) (p < 0.001). Subject group-2 was characterized with the most asthmatics (86%) and CRSwNP (100%) patients, and was associated with analyte cluster-2 (Th2; p < 0.001). Subject group-3 was associated with both analyte cluster-1 (Th1/Th17) and analyte cluster-3 (CC/GF) (p < 0.001), and had the highest proportion of CRSsNP patients (62.5%). Tissue levels of MBP, eosinophilia, and computed tomography (CT) scores were significantly higher in subject group-2 vs other groups (p ≤ 0.05). CONCLUSION: An unbiased network-mapping approach using a commercially available immunoassay kit reveals 3 distinct tissue cytokine-chemokine signatures that endotype CRS patients and controls. These signatures are prominent even in a limited number of patients, and may help formulate individualized therapy and optimize outcomes.

An immunologic test for chronic rhinosinusitis based on free intranasal eosinophilic major basic protein.

BACKGROUND: A histologic hallmark of chronic rhinosinusitis (CRS) is an eosinophilic inflammation, present with and without nasal polyposis and independent of atopy. Eosinophils migrate through nasal tissue including the epithelium into the nasal airway mucus, where they form clusters and degranulate, releasing granule proteins including the toxic major basic protein (MBP). Specific biomarkers for CRS, which could be used as a diagnostic test for CRS with a high sensitivity and specificity, are presently lacking. Recently, an enzyme-linked immunosorbent assay (ELISA)-based test for MBP in nasal airway mucus received regulatory approval. METHODS: A new assay was specifically developed to detect released MBP in airway mucus. MBP levels in nasal mucus of 85 randomly selected CRS patients diagnosed by endoscopy, computed tomography (CT) scans and symptoms were compared to 13 healthy controls and 5 disease controls (allergic rhinitis). RESULTS: Overall, 92% (78/85) of CRS patients' mucus were positive for MBP (mean 7722 ng/mL) vs none of 13 healthy controls and none of 5 allergic rhinitis patients (<7.8 ng/mL; p < 0.000000000002). In this study, the MBP ELISA had a 92% sensitivity and 100% specificity for CRS. CONCLUSION: Free MBP in nasal mucus can be used as a biomarker to diagnose CRS. The MBP ELISA represents the first immunologically-based test to potentially distinguish CRS from the eosinophilic inflammation in allergic rhinitis.

Regulation of TLR2 expression and function in human airway epithelial cells.

Toll-like receptor (TLR1-6) mRNAs are expressed in normal human bronchial epithelial cells with higher basal levels of TLR3. TLR2 mRNA and plasma membrane protein expression was enhanced by pretreatment with Poly IC, a synthetic double-stranded RNA (dsRNA) known to activate TLR3. Poly IC also enhanced mRNA expression of adaptor molecules (MyD88 and TIRAP) and coreceptors (Dectin-1 and CD14) involved in TLR2 signaling. Additionally, mRNA expression of TLR3 and dsRNA-sensing proteins MDA5 and RIG-I increased following Poly IC treatment. In contrast, basal mRNA expression of TLR5 and TLR2 coreceptor CD36 was reduced by 77% and 62%, respectively. ELISA of apical and basolateral solutions from Poly IC-stimulated monolayers revealed significantly higher levels of IL-6 and GM-CSF compared with the TLR2 ligand PAM(3)CSK(4). Pretreatment with anti-TLR2 blocking antibody inhibited the PAM(3)CSK(4)-induced increase in IL-6 secretion after Poly IC exposure. An increase in IL-6 secretion was also observed in cells stimulated with Alternaria extract after pretreatment with Poly IC. However, IL-6 secretion was not stimulated by zymosan or lipothechoic acid (LTA). These data demonstrated that upregulation of TLR2 following exposure to dsRNA enhances functional responses of the airway epithelium to certain (PAM(3)CSK(4)), but not all (zymosan, LTA) TLR2 ligands and that this is likely due to differences in coreceptor expression.

IL-33-activated dendritic cells induce an atypical TH2-type response.

BACKGROUND: IL-33, a recently discovered IL-1 family cytokine, is implicated in the development of T(H)2-type responses in vivo. However, the cellular targets for IL-33 are poorly understood. OBJECTIVE: We tested the hypotheses that dendritic cells (DCs) respond to IL-33 and that IL-33-activated DCs prime naive CD4(+) T cells to produce T(H)2-type cytokines. METHODS: Dendritic cells were derived from mouse bone marrow, and their expression of the IL-33 receptor, ST2, was examined by fluorescence-activated cell sorting and real-time RT-PCR. The DCs' responses to IL-33 were examined by fluorescence-activated cell sorting (MHC-II and CD86 expression) and by ELISA (IL-6 and IL-12 production). The ability of IL-33-activated DCs to prime naive T cells was assessed by coculture with isolated CD4(+) T cells and by measuring cytokines in the supernatants. RESULTS: ST2 mRNA was detectable in highly purified DCs. ST2 protein was abundant within DCs, but was barely detectable on their cell surfaces. Incubation of DCs with IL-33 increased their expression of MHC-II and CD86 and production of IL-6, but IL-12 was not produced. Anti-ST2 antibody inhibited IL-6 production from IL-33-activated DCs by approximately 60%; anti-ST2 did not affect IL-6 production from LPS-activated DCs. When incubated with naive CD4(+) T cells alone, IL-33 failed to stimulate cytokine production. In contrast, naive CD4(+) T cells incubated with IL-33-activated DCs showed robust production of IL-5 and IL-13, but IL-4 and IFN-gamma were undetectable. CONCLUSION: Dendritic cells respond directly to IL-33 through ST2. The IL-33 and DC interaction may represent a new pathway to initiate T(H)2-type immune responses.

Pimecrolimus reduces eosinophil activation associated with calcium mobilization.

BACKGROUND: Pimecrolimus is a calcineurin inhibitor that inhibits T cell and mast cell activation and effectively treats atopic dermatitis. However, its effects on eosinophils, a cell type implicated in allergic disease pathology, are unknown. Therefore, we examined the effects of pimecrolimus on eosinophil superoxide anion production, degranulation and survival. METHODS: Purified eosinophils from normal or atopic donors were incubated with serial dilutions of pimecrolimus (microM to nM) and then stimulated with platelet activating factor (PAF), interleukin 5 (IL5), secretory immunoglobulin A (sIgA) or Alternaria alternata (Alt) fungus extract. Eosinophil activation was monitored by cytochrome c reduction resulting from superoxide anion production and by a 2-site immunoassay for eosinophil-derived neurotoxin (EDN) in cellular supernatants, as a marker of degranulation. Eosinophil survival was measured by propidium iodide exclusion using flow cytometry after 4 days in culture. RESULTS: Normal and atopic eosinophil superoxide anion production induced by PAF, and associated with increased intracellular calcium, was inhibited up to 37% with 1 microM pimecrolimus. However, superoxide anion production induced by IL5 and sIgA was not consistently inhibited. EDN release, which ultimately depends on calcium, was inhibited about 30% with PAF, IL5 and sIgA stimulation for normal and atopic donor eosinophils. Furthermore, calcium-dependent Alt-induced EDN release was inhibited up to 49% with nanomolar pimecrolimus. Finally, increased eosinophil survival promoted by IL5 and sIgA was not influenced by pimecrolimus. CONCLUSION: Pimecrolimus moderately inhibits eosinophil superoxide anion production and EDN release associated with calcium mobilization, which may contribute to its efficacy in treating atopic dermatitis.

Clinical correlates of serum pro-major basic protein in a spectrum of eosinophilic disorders and myelofibrosis.

BACKGROUND/AIMS: Eosinophil cytoplasmic granules contain major basic protein (MBP), which is primarily translated from its precursor, proMBP. In this study, we evaluated the plasma level of proMBP in eosinophilic and chronic myeloproliferative disorders (MPN). METHODS: The levels of plasma proMBP were measured by radioimmunoassay in 25 healthy controls, 23 patients with systemic mastocytosis (SM), 11 patients with idiopathic eosinophilia (IE) and a cohort of 170 patients with MPN which included 76 patients with de novo myelofibrosis, 42 with polycythemia vera (PV), 17 with postpolycythemic myeloid metaplasia (Post-PV MF), 21 with essential thrombocythemia (ET) and 14 with postthrombocythemic myeloid metaplasia (Post-ET MF). RESULTS: The plasma proMBP level was significantly higher in patients with SM with eosinophilia (p < 0.001), IE (p < 0.001) and MPN with eosinophilia (p = 0.002) than in healthy controls. The median proMBP level of Post-PV MF and Post-ET MF patients was significantly higher than in PV and ET patients (p < 0.001 and p = 0.009, respectively). In IE patients, elevated proMBP was significantly correlated with the presence of splenomegaly (p < 0.05). In 76 de novo myelofibrosis patients, the proMBP level was correlated with spleen size and the presence of hypercatabolic symptoms. CONCLUSION: The significantly elevated levels of proMBP in myelofibrosis patients implies that proMBP could be an important stromal cytokine in bone marrow fibrosis.