A functional polymorphism in IL-18 is associated with severity of bronchial asthma

Low Serum IL-18 Levels May Predict the Effectiveness of Dupilumab in Severe Asthma

Objective Dupilumab, a monoclonal antibody specific for the human interleukin (IL)-4 receptor α, is used to treat severe asthma, especially in patients with elevated blood eosinophil counts and fractional exhaled nitric oxide (FeNO). The therapeutic response to dupilumab is highly variable. In this study, we explored new serum biomarkers to accurately predict the effect of dupilumab and examine the effect of dupilumab based on changes in the clinical parameters and cytokine levels. Methods Seventeen patients with severe asthma treated with dupilumab were enrolled. Responders, defined as those with a >0.5-point decrease in the Asthma Control Questionnaire (ACQ) score after 6 months of treatment, were included. Results There were 10 responders and 7 non-responders. Serum type 2 cytokines were equivalent between responders and non-responders; the baseline serum IL-18 level was significantly lower in responders than in non-responders (responders, 194.9±51.0 pg/mL; non-responders, 323.4±122.7 pg/mL, p=0.013). The cut-off value of IL-18 at 230.5 pg/mL could be used to distinguish non-responders from responders (sensitivity 71.4, specificity 80.0, p=0.032). Conclusion A low baseline serum IL-18 level may be a useful predictor of an unfavorable response to dupilumab in terms of the ACQ-6.

Distinct Epithelial-Innate Immune Cell Transcriptional Circuits Underlie Airway Hyperresponsiveness in Asthma

Rationale: Indirect airway hyperresponsiveness (AHR) is a highly specific feature of asthma, but the underlying mechanisms responsible for driving indirect AHR remain incompletely understood. Objectives: To identify differences in gene expression in epithelial brushings obtained from individuals with asthma who were characterized for indirect AHR in the form of exercise-induced bronchoconstriction (EIB). Methods: RNA-sequencing analysis was performed on epithelial brushings obtained from individuals with asthma with EIB (n = 11) and without EIB (n = 9). Differentially expressed genes (DEGs) between the groups were correlated with measures of airway physiology, sputum inflammatory markers, and airway wall immunopathology. On the basis of these relationships, we examined the effects of primary airway epithelial cells (AECs) and specific epithelial cell-derived cytokines on both mast cells (MCs) and eosinophils (EOS). Measurements and Main Results: We identified 120 DEGs in individuals with and without EIB. Network analyses suggested critical roles for IL-33-, IL-18-, and IFN-γ-related signaling among these DEGs. IL1RL1 expression was positively correlated with the density of MCs in the epithelial compartment, and IL1RL1, IL18R1, and IFNG were positively correlated with the density of intraepithelial EOS. Subsequent ex vivo modeling demonstrated that AECs promote sustained type 2 (T2) inflammation in MCs and enhance IL-33-induced T2 gene expression. Furthermore, EOS increase the expression of IFNG and IL13 in response to both IL-18 and IL-33 as well as exposure to AECs. Conclusions: Circuits involving epithelial interactions with MCs and EOS are closely associated with indirect AHR. Ex vivo modeling indicates that epithelial-dependent regulation of these innate cells may be critical in indirect AHR and modulating T2 and non-T2 inflammation in asthma.

Role of inflammasome in severe, steroid-resistant asthma

Purpose of review

Asthma is a common heterogeneous group of chronic inflammatory diseases with different pathological phenotypes classified based on the various clinical, physiological and immunobiological profiles of patients. Despite similar clinical symptoms, asthmatic patients may respond differently to treatment. Hence, asthma research is becoming more focused on deciphering the molecular and cellular pathways driving the different asthma endotypes. This review focuses on the role of inflammasome activation as one important mechanism reported in the pathogenesis of severe steroid resistant asthma (SSRA), a Th2-low asthma endotype. Although SSRA represents around 5-10% of asthmatic patients, it is responsible for the majority of asthma morbidity and more than 50% of asthma associated healthcare costs with clear unmet need. Therefore, deciphering the role of the inflammasome in SSRA pathogenesis, particularly in relation to neutrophil chemotaxis to the lungs, provides a novel target for therapy.

Recent findings

The literature highlighted several activators of inflammasomes that are elevated during SSRA and result in the release of proinflammatory mediators, mainly IL-1β and IL-18, through different signaling pathways. Consequently, the expression of NLRP3 and IL-1β is shown to be positively correlated with neutrophil recruitment and negatively correlated with airflow obstruction. Furthermore, exaggerated NLRP3 inflammasome/IL-1β activation is reported to be associated with glucocorticoid resistance.

Summary

In this review, we summarized the reported literature on the activators of the inflammasome during SSRA, the role of IL-1β and IL-18 in SSRA pathogenesis, and the pathways by which inflammasome activation contributes to steroid resistance. Finally, our review shed light on the different levels to target inflammasome involvement in an attempt to ameliorate the serious outcomes of SSRA.

Rhinovirus infection of the airway epithelium enhances mast cell immune responses via epithelial-derived interferons

BACKGROUND

Mast cells (MCs) within the airway epithelium in asthma are closely related to airway dysfunction, but cross talk between airway epithelial cells (AECs) and MCs in asthma remains incompletely understood. Human rhinovirus (RV) infections are key triggers for asthma progression, and AECs from individuals with asthma may have dysregulated antiviral responses.

OBJECTIVE

We utilized primary AECs in an ex vivo coculture model system to examine cross talk between AECs and MCs after epithelial rhinovirus infection.

METHODS

Primary AECs were obtained from 11 children with asthma and 10 healthy children, differentiated at air-liquid interface, and cultured in the presence of laboratory of allergic diseases 2 (LAD2) MCs. AECs were infected with rhinovirus serogroup A 16 (RV16) for 48 hours. RNA isolated from both AECs and MCs underwent RNA sequencing. Direct effects of epithelial-derived interferons on LAD2 MCs were examined by real-time quantitative PCR.

RESULTS

MCs increased expression of proinflammatory and antiviral genes in AECs. AECs demonstrated a robust antiviral response after RV16 infection that resulted in significant changes in MC gene expression, including upregulation of genes involved in antiviral responses, leukocyte activation, and type 2 inflammation. Subsequent ex vivo modeling demonstrated that IFN-β induces MC type 2 gene expression. The effects of AEC donor phenotype were small relative to the effects of viral infection and the presence of MCs.

CONCLUSIONS

There is significant cross talk between AECs and MCs, which are present in the epithelium in asthma. Epithelial-derived interferons not only play a role in viral suppression but also further alter MC immune responses including specific type 2 genes.

Anti-inflammatory activities of Qingfei oral liquid and its influence on respiratory microbiota in mice with ovalbumin-induced asthma

Dysbiosis of respiratory microbiota is closely related to the pathophysiological processes of asthma, including airway inflammation. Previous studies have shown that Qingfei oral liquid (QF) can alleviate airway inflammation and airway hyper-responsiveness in respiratory syncytial virus-infected asthmatic mice, but its effect on the respiratory microbiota is unknown. We therefore aimed to observe the effects of QF on airway inflammation and respiratory microbiota in ovalbumin (OVA)-induced asthmatic mice. We also explored the potential mechanism of QF in reducing airway inflammation by regulating respiratory microbiota. Hematoxylin and eosin as well as periodic acid-Schiff staining were performed to observe the effects of QF on lung pathology in asthmatic mice. Cytokine levels in bronchoalveolar lavage fluid (BALF) specimens were also measured. Changes in respiratory microbiota were analyzed using 16S rRNA gene sequencing, followed by taxonomical analysis. In order to verify the metagenomic function prediction results, the expression of key proteins related to the MAPK and NOD-like receptor signaling pathways in the lung tissues were detected by immunohistochemistry. The current study found that QF had a significant anti-inflammatory effect in the airways of asthmatic mice. This is mainly attributed to a reduction in lung pathology changes and regulating cytokine levels in BALF. Analysis of the respiratory microbiota in asthmatic mice showed that the abundance of Proteobacteria at the phylum level and Pseudomonas at the genus level increased significantly and QF could significantly regulate the dysbiosis of respiratory microbiota in asthmatic mice. Metagenomic functional prediction showed that QF can downregulate the MAPK and Nod-like receptor signaling pathways. Immunohistochemical results showed that QF could downregulate the expression of p-JNK, p-P38, NLRP3, Caspase-1, and IL-1β, which are all key proteins in the signaling pathway of lung tissue. Our study therefore concluded that QF may reduce airway inflammation in asthmatic mice by regulating respiratory microbiota, and to the possibly downregulate MAPK and Nod-like receptor signaling pathways as its underlying mechanism.

Machine learning implicates the IL-18 signaling axis in severe asthma

Asthma is a common disease with profoundly variable natural history and patient morbidity. Heterogeneity has long been appreciated, and much work has focused on identifying subgroups of patients with similar pathobiological underpinnings. Previous studies of the Severe Asthma Research Program (SARP) cohort linked gene expression changes to specific clinical and physiologic characteristics. While invaluable for hypothesis generation, these data include extensive candidate gene lists that complicate target identification and validation. In this analysis, we performed unsupervised clustering of the SARP cohort using bronchial epithelial cell gene expression data, identifying a transcriptional signature for participants suffering exacerbation-prone asthma with impaired lung function. Clinically, participants in this asthma cluster exhibited a mixed inflammatory process and bore transcriptional hallmarks of NF-κB and activator protein 1 (AP-1) activation, despite high corticosteroid exposure. Using supervised machine learning, we found a set of 31 genes that classified patients with high accuracy and could reconstitute clinical and transcriptional hallmarks of our patient clustering in an external cohort. Of these genes, IL18R1 (IL-18 Receptor 1) negatively associated with lung function and was highly expressed in the most severe patient cluster. We validated IL18R1 protein expression in lung tissue and identified downstream NF-κB and AP-1 activity, supporting IL-18 signaling in severe asthma pathogenesis and highlighting this approach for gene and pathway discovery.

Immunological Roles of NLR in Allergic Diseases and Its Underlying Mechanisms

Our understanding on the immunological roles of pathogen recognition in innate immunity has vastly increased over the past 20 years. Nucleotide-binding oligomerization domain (NOD)-like receptors (NLR) are cytosolic pattern recognition receptors (PRR) that are responsible for sensing microbial motifs and endogenous damage signals in mammalian cytosol for immune surveillance and host defense. The accumulating discoveries on these NLR sensors in allergic diseases suggest that the pathogenesis of allergic diseases may not be confined to the adaptive immune response. Therapy targeting NLR in murine models also shields light on its potential in the treatment of allergies in man. In this review, we herein summarize the recent understanding of the role of NLR sensors and their molecular mechanisms involved in allergic inflammation, including atopic dermatitis and allergic asthma.

High serum free IL-18 is associated with decreased omalizumab efficacy: findings from a 2-year omalizumab treatment study

OBJECTIVE

Omalizumab is more effective in severe allergic patients with eosinophilic asthma than those with non-eosinophilic asthma. IL-18, a unique cytokine involved in allergic but non-eosinophilic inflammation, might be associated with the latter condition. We aimed to clarify the roles of IL-18 related pathways in insufficient response to omalizumab treatment.

METHODS

Patients with severe allergic asthma who completed 2-year omalizumab treatments at Kyoto University Hospital were included in this study (UMIN000002389). Associations between pretreatment levels of serum free IL-18 in addition to other mediators and asthma phenotypes including responses to omalizumab treatment were analyzed. Changes in serum free IL-18, periostin and total IgE levels during the treatment were also examined.

RESULTS

Twenty-seven patients (19 females, average age of 55.7 years) were examined. Fifteen incomplete responders who experienced exacerbations in the second year, were significantly and more frequently obese and showed significantly earlier asthma onset, lower blood eosinophils and more exacerbations before omalizumab treatment than complete responders. Significantly more patients showed high baseline serum free IL-18 levels (≥141 pg/mL, a threshold for the highest tertile) among the incomplete responders than complete responders. Patients with high serum free IL-18 levels shared similar characteristics with incomplete responders, showing significant reductions in serum total IgE levels during omalizumab treatment. Finally, serum free IL-18 levels negatively correlated with serum periostin levels at baseline and in change ratios.

CONCLUSIONS

High baseline serum free IL-18 levels may predict reduced omalizumab efficacy in severe allergic patients with type-2 low asthma, regarding reduction of exacerbations.

Interleukin-18: Biological properties and role in disease pathogenesis

Initially described as an interferon (IFN)γ‐inducing factor, interleukin (IL)‐18 is indeed involved in Th1 and NK cell activation, but also in Th2, IL‐17‐producing γδ T cells and macrophage activation. IL‐18, a member of the IL‐1 family, is similar to IL‐1β for being processed by caspase 1 to an 18 kDa‐biologically active mature form. IL‐18 binds to its specific receptor (IL‐18Rα, also known as IL‐1R7) forming a low affinity ligand chain. This is followed by recruitment of the IL‐18Rβ chain. IL‐18 then uses the same signaling pathway as IL‐1 to activate NF‐kB and induce inflammatory mediators such as adhesion molecules, chemokines and Fas ligand. IL‐18 also binds to the circulating high affinity IL‐18 binding protein (BP), such as only unbound free IL‐18 is active. IL‐18Rα may also bind IL‐37, another member of the IL‐1 family, but in association with the negative signaling chain termed IL‐1R8, which transduces an anti‐inflammatory signal. IL‐18BP also binds IL‐37 and this acts as a sink for the anti‐inflammatory properties of IL‐37. There is now ample evidence for a role of IL‐18 in various infectious, metabolic or inflammatory diseases such as influenza virus infection, atheroma, myocardial infarction, chronic obstructive pulmonary disease, or Crohn's disease. However, IL‐18 plays a very specific role in the pathogenesis of hemophagocytic syndromes (HS) also termed Macrophage Activation Syndrome. In children affected by NLRC4 gain‐of‐function mutations, IL‐18 circulates in the range of tens of nanograms/mL. HS is treated with the IL‐1 Receptor antagonist (anakinra) but also specifically with IL‐18BP. Systemic juvenile idiopathic arthritis or adult‐onset Still's disease are also characterized by high serum IL‐18 concentrations and are treated by IL‐18BP.

Altered expression of IL-18 binding protein and IL-18 receptor in basophils and mast cells of asthma patients

IL-18 is likely to contribute to asthma. However, little is known regarding the role of IL-18 binding protein (BP) and IL-18 receptor (R) in asthma. Because the action of IL-18 in the body is regulated by IL-18BP and mast cells and basophils are key cell types involved in asthma, we investigated the expression of IL-18, IL-18BP and IL-18R in basophils and mast cells using flow cytometry and a mouse asthma model. We found that among basophils, approximately 53% and 51% were IL-18⁺ , 85% and 81% were IL-18BP⁺ basophils, and 19.8% and 8.6% were IL-18R⁺ in healthy control (HC) and asthmatic blood, respectively. The allergens tested had little effect on the expression of IL-18 and related factors. Only 3.5%, 14.3% and 2.4% of dispersed mast cells expressed IL-18, IL-18BP and IL-18R, respectively, in asthmatic sputum. In a mouse asthma model, OVA-sensitized mice exhibited decreased IL-18BP⁺ but increased IL-18R⁺ basophils in their blood. IL-18 increased the number of basophils but eliminated IL-18BP⁺ basophils in mouse blood. IL-18 increased the number of mast cells and IL-18R⁺ mast cells in the lung as well as increased the mast cell numbers and IL-18BP⁺ mast cells in the bronchoalveolar lavage fluid (BALF) of OVA-sensitized mice. Thus, basophils and mast cells may be involved in asthma pathogenesis via an IL-18-associated mechanism.

Role of IL-18 in atopic asthma is determined by balance of IL-18/IL-18BP/IL-18R

It is recognized that IL‐18 is related to development of asthma, but role of IL‐18 in asthma remains controversial and confusing. This is largely due to lack of information on expression of IL‐18 binding protein (BP) and IL‐18 receptor (R) in asthma. In this study, we found that plasma levels of IL‐18 and IL‐18BP were elevated in asthma. The ratio between plasma concentrations of IL‐18 and IL‐18BP was 1:12.8 in asthma patients. We demonstrated that 13‐fold more monocytes, 17.5‐fold more neutrophils and 4.1‐fold more B cells express IL‐18BP than IL‐18 in asthmatic blood, suggesting that there is excessive amount of IL‐18BP to abolish actions of IL‐18 in asthma. We also discovered that more IL‐18R+ monocytes, neutrophils and B cells are located in asthmatic blood. Once injected, IL‐18 eliminated IL‐18R+ monocytes in blood, but up‐regulated expression of IL‐18R in lung macrophages of OVA‐sensitized mice. Our data clearly indicate that the role of IL‐18 in asthma is very likely to be determined by balance of IL‐18/IL‐18BP/IL‐18R expression in inflammatory cells. Therefore, IL‐18R blocking or IL‐18BP activity enhancing therapies may be useful for treatment of asthma.

Association of interleukin-18 and asthma

Cytokine-mediated immunity plays a dominant role in the pathogenesis of various immune diseases, including asthma. The recent identification of the family interleukin (IL)-1-related cytokine IL-18 now contributes to our understanding of the fine-tuning of cellular immunity. IL-18 can act as a cofactor for Th2 cell development and IgE production and also plays an important role in the differentiation of Th1 cells. Recent work identified an IL-18 association with the pathogenesis of asthma, wherein increased IL-18 expression was found in the serum of patients. Furthermore, IL-18 polymorphisms with susceptibility to asthma were reported, suggesting that IL-18 may be therapeutically relevant to asthma. In this review, we discuss the role of IL-18 in the pathogenesis of asthma and its therapeutic potential based on current research.

Influence of IL-18 and IL-10 Polymorphisms on Tacrolimus Elimination in Chinese Lung Transplant Patients

Aims. The influence of interleukin-10 (IL-10) and interleukin-18 (IL-18) polymorphisms on tacrolimus pharmacokinetics had been described in liver and kidney transplantation. The expression of cytokines varied in different kinds of transplantation. The influence of IL-10 and IL-18 genetic polymorphisms on the pharmacokinetic parameters of tacrolimus remains unclear in lung transplantation. Methods. 51 lung transplant patients at Shanghai Pulmonary Hospital were included. IL-18 polymorphisms (rs5744247 and rs1946518), IL-10 polymorphisms (rs1800896, rs1800872, and rs3021097), and CYP3A5 rs776746 were genotyped. Dose-adjusted trough blood concentrations (C/D ratio, mg/kg body weight) in lung transplant patients during the first 4 postoperative weeks were calculated. Results. IL-18 rs5744247 allele C and rs1946518 allele A were associated with fast tacrolimus metabolism. Combined analysis showed that the numbers of low IL-18 mRNA expression alleles had positive correlation with tacrolimus C/D ratios in lung transplant recipients. The influence of IL-18 polymorphisms on tacrolimus C/D ratios was observed in CYP3A5 expresser recipients, but not in CYP3A5 nonexpresser recipients. No clinical significance of tacrolimus C/D ratios difference of IL-10 polymorphisms was found in our data. Conclusions. IL-18 polymorphisms may influence tacrolimus elimination in lung transplantation patients.

Future treatment for asthma

The landscape of asthma has considerably changed after 40 years of inhaled corticosteroid development and nearly 20 years since the first monoclonal antibodies (mAbs) were approved. New members of pharmacological families and more effective drug-delivery devices have been designed but the proportion of uncontrolled patients, unfortunately, remains stable. The most promising treatments now rely on targeted therapies that encourage the improvement of the characterisation of our patients. These clinical (phenotype) or new biological (endotype) tools lead to palpable personalised medicine. This review examines not only the future of mAbs and other new ways of treating asthma but also describes futuristic views based on the paradigm shifts that are ready to occur.

An Interleukin 13 Polymorphism Is Associated with Symptom Severity in Adult Subjects with Ever Asthma

Different genes are associated with categorical classifications of asthma severity. However, continuous outcomes should be used to catch the heterogeneity of asthma phenotypes and to increase the power in association studies. Accordingly, the aim of this study was to evaluate the association between single nucleotide polymorphisms (SNPs) in candidate gene regions and continuous measures of asthma severity, in adult patients from the general population. In the Gene Environment Interactions in Respiratory Diseases (GEIRD) study (www.geird.org), 326 subjects (aged 20–64) with ever asthma were identified from the general population in Verona (Italy) between 2007 and 2010. A panel of 236 SNPs tagging 51 candidate gene regions (including one or more genes) was analysed. A symptom and treatment score (STS) and pre-bronchodilator FEV₁% predicted were used as continuous measures of asthma severity. The association of each SNP with STS and FEV₁% predicted was tested by fitting quasi-gamma and linear regression models, respectively, with gender, body mass index and smoking habits as potential confounders. The Simes multiple-test procedure was used for controlling the false discovery rate (FDR). SNP rs848 in the IL13 gene region (IL5/RAD50/IL13/IL4) was associated with STS (TG/GG vs TT genotype: uncorrected p-value = 0.00006, FDR-corrected p-value = 0.04), whereas rs20541 in the same gene region, in linkage disequilibrium with rs848 (r² = 0.94) in our sample, did not reach the statistical significance after adjusting for multiple testing (TC/CC vs TT: uncorrected p-value = 0.0003, FDR-corrected p-value = 0.09). Polymorphisms in other gene regions showed a non-significant moderate association with STS (IL12B, TNS1) or lung function (SERPINE2, GATA3, IL5, NPNT, FAM13A) only. After adjusting for multiple testing and potential confounders, SNP rs848 in the IL13 gene region is significantly associated with a continuous measure of symptom severity in adult subjects with ever asthma.

Correlation of IL-18 with Tryptase in Atopic Asthma and Induction of Mast Cell Accumulation by IL-18

Interleukin- (IL-) 18 and tryptase were previously reported to relate to asthma, but the correlation between these two potent proinflammatory molecules in asthma and their roles in mast cell accumulation remain uninvestigated. Using flow cytometric analysis technique and ovalbumin- (OVA-) sensitized mouse model, it was found that IL-18 and tryptase levels in the plasma of moderate and severe asthma were elevated, and they correlated well with each other. Tryptase and agonist peptides of protease activated receptor- (PAR-) 2 induced substantial quantity of IL-18 release. IL-18 and tryptase provoked mast cell accumulation in peritoneum of OVA-sensitized mice. OVA-sensitization increased number of IL-18 receptor (R)⁺ mast cells. IL-18 and tryptase induced dramatic increase in IL-18R⁺ mast cells and mean fluorescence intensity (MFI) of IL-18R on mast cells. Moreover, while IL-18 induced an increase in PAR-2⁺ mast cells in nonsensitized mice, IL-18 and tryptase provoked increases in IL-4 and thymic stromal lymphopoietin (TSLP) in the peritoneum of OVA-sensitized mice. In summary, the correlation between IL-18 and tryptase in plasma of patients with asthma indicates close interactions between them, which should be considered for development of anti-IL-18 and antitryptase therapies. Interactions between IL-18 and tryptase may contribute to mast cell recruitment in asthma.

The Inflammatory Caspases-1 and -11 Mediate the Pathogenesis of Dermatitis in Sharpin-Deficient Mice

Chronic proliferative dermatitis in mice (cpdm) is a spontaneous multiorgan inflammatory disorder with pathological hallmarks similar to atopic dermatitis and psoriasis in humans. Cpdm mice lack expression of SHANK-associated RH domain-interacting protein, an adaptor of the linear ubiquitin assembly complex, which acts in the NF-κB pathway to promote inflammation and protect from apoptosis and necroptosis. Although skin inflammation in cpdm mice is driven by TNF- and RIPK1-induced cell death, the contribution of initiating innate immunity sensors and additional inflammatory pathways remains poorly characterized. In this article, we show that inflammasome signaling, including the expression and activation of the inflammatory caspase-1 and -11 and IL-1 family cytokines, was highly upregulated in the skin of cpdm mice prior to overt disease onset. Genetic ablation of caspase-1 and -11 from cpdm mice significantly reduced skin inflammation and delayed disease onset, whereas systemic immunological disease persisted. Loss of Nlrp3 also attenuated skin disease, albeit more variably. Strikingly, induction of apoptosis and necroptosis effectors was sharply decreased in the absence of caspase-1 and -11. These results position the inflammasome as an important initiating signal in skin disease pathogenesis and provide novel insights about inflammasome and cell death effector cross-talk in the context of inflammatory diseases.

Genomewide association study identifies HAS2 as a novel susceptibility gene for adult asthma in a Japanese population

BACKGROUND

It is increasingly clear that asthma is not a single disease, but a disorder with vast heterogeneity in pathogenesis, severity, and treatment response. To date, 30 genomewide association studies (GWASs) of asthma have been performed, including by our group. However, most gene variants identified so far confer relatively small increments in risk and explain only a small proportion of familial clustering.

OBJECTIVE

To identify additional genetic determinants of susceptibility to asthma using a selected Japanese population with reduced tobacco smoking exposure.

METHODS

We performed a GWAS by genotyping a total of 480 098 single-nucleotide polymorphisms (SNPs) for a Japanese cohort consisting of 734 healthy controls and 240 patients with asthma who had smoked for no more than 10 pack-years. The SNP with the strongest association was genotyped in two other independent Japanese cohorts consisting of a total of 531 healthy controls and 418 patients with asthma who had smoked for no more than 10 pack-years. For the hyaluronan synthase 2 (HAS2) gene, we investigated SNP-gene associations using an expression quantitative trait loci (eQTL) database and also analysed its gene expression profiles in 13 different normal tissues.

RESULTS

In the discovery GWAS, a SNP located upstream of HAS2, rs7846389, showed the strongest statistical significance (P = 1.43 × 10(-7) ). In the two independent replication cohorts, rs7846389 was consistently associated with asthma (nominal P = 0.0152 and 0.0478 in the first and second replication cohorts, respectively). In the meta-analysis, association of rs7846389 with susceptibility to asthma reached the level of genomewide significance (P = 7.92 × 10(-9) ). This variant was strongly correlated with HAS2 mRNA expression. The strongest expression of the gene was detected in the lung.

CONCLUSIONS

Our study identified HAS2 as a novel candidate gene for susceptibility to adult asthma.

Alternaria extract activates autophagy that induces IL-18 release from airway epithelial cells

Alternaria alternata is a major outdoor allergen that causes allergic airway diseases. Alternaria extract (ALT-E) has been shown to induce airway epithelial cells to release IL-18 and thereby initiate Th2-type responses. We investigated the underlying mechanisms involved in IL-18 release from ALT-E-stimulated airway epithelial cells. Normal human bronchial epithelial cells and A549 human lung adenocarcinoma cells were stimulated with ALT-E in the presence of different inhibitors of autophagy or caspases. IL-18 levels in culture supernatants were measured by ELISA. The numbers of autophagosomes, an LC3-I to LC3-II conversion, and p62 degradation were determined by immunofluorescence staining and immunoblotting. 3-methyladenine and bafilomycin, which inhibit the formation of preautophagosomal structures and autolysosomes, respectively, suppressed ALT-E-induced IL-18 release by cells, whereas caspase 1 and 8 inhibitors did not. ALT-E-stimulation increased autophagosome formation, LC-3 conversion, and p62 degradation in airway epithelial cells. LPS-stimulation induced the LC3 conversion in A549 cells, but did not induce IL-18 release or p62 degradation. Unlike LPS, ALT-E induced airway epithelial cells to release IL-18 via an autophagy dependent, caspase 1 and 8 independent pathway. Although autophagy has been shown to negatively regulate canonical inflammasome activity in TLR-stimulated macrophages, our data indicates that this process is an unconventional mechanism of IL-18 secretion by airway epithelial cells.

Low interleukin (IL)-18 levels in sputum supernatants of patients with severe refractory asthma

BACKGROUND

Severe refractory asthma (SRA) is characterized by persistent asthma symptoms, amplified airway inflammation despite treatment with high dose inhaled steroids and increased airway bacterial colonization. Interleukin (IL)-18 is a pleiotropic pro-inflammatory cytokine that modulates airway inflammation. Furthermore, as a product of the inflammasome, IL-18 is involved in host defence against viral and bacterial stimuli by modulating the immune response.

OBJECTIVE

To determine IL-18 levels in sputum supernatants of patients with asthma and to investigate whether underlying severity affects its levels. Furthermore, possible associations with atopy and mediators and cells involved in the inflammatory process of the airways were examined.

METHODS

Forty-five patients with mild intermittent asthma (21 smokers) and 18 patients with SRA in stable state were studied. All subjects underwent lung function tests, skin prick tests, and sputum induction for cell count identification. IL-18 and ECP levels were measured in sputum supernatants. Furthermore, sputum samples were examined for the commonest respiratory pathogens and viruses by real time polymerase chain reaction (RT-PCR).

RESULTS

Patients with SRA had significantly lower IL-18 levels in sputum supernatants compared to mild asthmatics (p < 0.001). Twelve out of eighteen patients with SRA were colonized by viruses and/or bacterial pathogens. IL-18 levels correlated with the percentage of macrophages (r = 0.635, p = 0.026) and inversely correlated with the percentage of neutrophils in sputum (r = -0.715, p = 0.009). No correlations were found between IL-18, ECP and the percentage of eosinophils in the sputum of SRA.

CONCLUSIONS

In SRA IL-18 is possibly involved in chronic airway inflammation through an eosinophil independent pathway. The decreased levels of IL-18 in SRA support the hypothesis of deregulated inflammasome activation, justifying the susceptibility of these patients for bacterial colonization or infection.

Donor IL-18 rs5744247 polymorphism as a new biomarker of tacrolimus elimination in Chinese liver transplant patients during the early post-transplantation period: results from two cohort studies

Aim: This study evaluated the relationships between IL-18 polymorphisms and tacrolimus elimination in Chinese liver transplant patients. Patients & methods: Eighty-four liver transplant patients from Shanghai (training set) and 50 patients from Shandong (validating set) were inculded. IL-18 polymorphisms (rs5744247, rs7106524, rs549908, rs187238 and rs1946518) and CYP3A5 rs776746 were genotyped. Results: In training set, daily drug dose, total bilirubin, donor CYP3A5 rs776746 and IL-18 rs5744247 genotypes were screened to construct prediction model for tacrolimus elimination. This model was confirmed in validating set (p < 0.001). Donor IL-18 rs5744247 polymorphism was an independent predictor of tacrolimus elimination in the first week after transplantation in both training (p = 0.008) and validating cohorts (p = 0.033). Conclusion: Donor IL-18 rs5744247 polymorphism may influence on tacrolimus elimination.

Original submitted 16 July 2014; Revision submitted 12 November 2014

The relationship between interleukin-18 polymorphisms and allergic disease: a meta-analysis

Recent studies have suggested that IL-18 −607C/A and −137G/C polymorphisms may be associated with the risk of allergic disease; however, individually published results are inconclusive. Therefore, we performed a meta-analysis to clarify whether IL-18 −607C/A and −137G/C polymorphisms were associated with the risk of allergic disease. A total of 21 studies including 5,331 cases and 9,658 controls were involved in this meta-analysis. In the overall analysis and the subgroup analysis according to ethnicity, we did not find significant association between IL-18 −607C/A or −137G/C polymorphism and the risk of allergic disease (all P > 0.05). However, in a stratified analysis by type of allergic disease, our results indicated that IL-18 −607C/A polymorphism was associated with a significantly decreased risk of allergic asthma in heterozygous comparison and IL-18 −137G/C was associated with a significantly decreased risk of allergic dermatitis in recessive model and homozygous comparison. In the stratified analysis by source of control, IL-18−607C/A showed significantly reduced risk in population-based subgroup, and for IL-18 −137G/C only significantly decreased risk was found in the hospital-based subgroup. Our meta-analysis suggests that IL-18 −607C/A and −137G/C polymorphisms may be protective factors for the risk of allergic asthma and allergic dermatitis, respectively.

Genome-wide association study for levels of total serum IgE identifies HLA-C in a Japanese population

Most of the previously reported loci for total immunoglobulin E (IgE) levels are related to Th2 cell-dependent pathways. We undertook a genome-wide association study (GWAS) to identify genetic loci responsible for IgE regulation. A total of 479,940 single nucleotide polymorphisms (SNPs) were tested for association with total serum IgE levels in 1180 Japanese adults. Fine-mapping with SNP imputation demonstrated 6 candidate regions: the PYHIN1/IFI16, MHC classes I and II, LEMD2, GRAMD1B, and chr13∶60576338 regions. Replication of these candidate loci in each region was assessed in 2 independent Japanese cohorts (n = 1110 and 1364, respectively). SNP rs3130941 in the HLA-C region was consistently associated with total IgE levels in 3 independent populations, and the meta-analysis yielded genome-wide significance (P = 1.07×10⁻¹⁰). Using our GWAS results, we also assessed the reproducibility of previously reported gene associations with total IgE levels. Nine of 32 candidate genes identified by a literature search were associated with total IgE levels after correction for multiple testing. Our findings demonstrate that SNPs in the HLA-C region are strongly associated with total serum IgE levels in the Japanese population and that some of the previously reported genetic associations are replicated across ethnic groups.

Interleukin-18 expression, CD8(+) T cells, and eosinophils in lungs of nonsmokers with fatal asthma

BACKGROUND

The process of airway inflammation in the lungs of nonsmokers who die of asthma (fatal asthma) has not been reported in detail.

OBJECTIVE

To examine nonsmokers who had died of asthma to exclude chronic obstructive pulmonary disease and investigate pulmonary inflammatory cells and the expression of interleukin-18 (IL-18) and its receptor in lung tissues compared with those in patients with well-controlled mild asthma and nonsmokers.

METHODS

Lung tissues were obtained at autopsy examination from 12 nonsmokers with fatal asthma, excluding cases of chronic obstructive pulmonary disease, and from 5 nonsmokers with well-controlled mild asthma and 10 nonsmokers who had undergone surgical resection for lung cancer. Pulmonary inflammatory cells were examined and the expression of the proinflammatory cytokine IL-18 and its receptor in the lungs was evaluated.

RESULTS

The numbers of eosinophils and lymphocytes, but not basophils or macrophages, were significantly increased in the lungs of patients with fatal asthma compared with the other 2 groups. The lung neutrophil count did not differ significantly between the fatal and mild asthma groups but was significantly higher in the fatal asthma group than in nonsmokers. CD8(+) T cells, but not CD4(+) T cells, were significantly increased in the lungs of the fatal asthma group compared with the other 2 groups. IL-18 protein and IL-18 receptor were strongly expressed in the lungs in the fatal asthma group.

CONCLUSION

Caspase-1 inhibitors, anti-IL-18 antibodies, anti-IL-18 receptor antibodies, IL-18 binding protein, or inhibitors of genes downstream of the IL-18 signal transduction pathway may be of clinical benefit for the treatment of patients with severe asthma.

Genetic analysis of asthma exacerbations

BACKGROUND

Identifying genetic markers of susceptibility to exacerbations may improve patient management, decrease morbidity, and lead to drug development.

OBJECTIVES

To assess whether genetic markers associated with severe asthma exacerbations in previous reports are associated with less severe events that do not require intensive care and intubation and to identify additional markers in candidate genes and throughout the genome.

METHODS

A total of 199 patients and 502 controls (individuals without an exacerbation) were identified from 4 clinical trials. We genotyped 51 markers from 17 genes previously reported to be associated with exacerbations; a whole genome scan was used to identify additional markers. Admixture analysis was conducted to characterize the presence of ancestral groups. The genetic marker effects were assessed by logistic regression for each study followed by a meta-analysis.

RESULTS

Several coding variants in the IL4R gene had a genetic effect across 3 studies, including rs1805011 in IL4R (P < .0006). In addition, 3 markers in the IFNB1 gene showed evidence of association (P < .002) but only in the study with African Americans. Because these markers did not meet the prespecified multiplicity-adjusted significance level of P = .0002, we were unable to confirm previously published results for less severe events. The whole genome scan identified genes related to mast cell mediator release. The admixture analysis suggests that ancestry was best characterized by the presence of 3 ancestral groups.

CONCLUSION

We were unable to confirm previously reported associations of genetic markers with asthma exacerbations. Although, in general, the patients studied had less severe asthma than patients in earlier reports, these results suggest involvement of similar pathways.

TRIAL REGISTRATION

clinicaltrials.gov Identifiers: NTC00452699, NCT00452348, NTC00102765, NCT00843193.

Gender-specific association of the interleukin 18 gene with symptomatic gallstone disease

BACKGROUND AND AIM

Symptomatic gallstone disease (SGSD) induced several inflammatory responses and affected extrahepatic bile ducts. Although the pathology and environmental risk factors of gallstone disease are well documented, immune or inflammatory responses in SGSD development are still inconclusive. Interleukin 18 (IL18) is a pro-inflammatory cytokine that plays an important role in immune, infectious, and inflammatory diseases because of the induction of interferon-γ. In this study, we investigated whether polymorphisms of the IL18 gene were associated with SGSD susceptibility.

METHODS

Genomic DNA was isolated from the whole blood samples of 445 patients with SGSD and 1121 gallstone-free controls. The IL18 rs549908T>G, rs5744247C>G, rs187238G>C, rs1946518T>G, and rs360719A>G polymorphisms were genotyped using predeveloped TaqMan allelic discrimination assay.

RESULTS

We found IL18 rs5744247G allele conferred protection against SGSD in female patients (odds ratio = 0.75, corrected P-value = 0.015). Haplotype analysis revealed that TGGTA protected females from SGSD development (odds ratio = 0.75, corrected P-value = 0.02).

CONCLUSIONS

Based on our findings, IL18 rs5744247C>G polymorphism could be a potential genetic marker to predict SGSD susceptibility in Han Chinese women.

Cytokines in chronic respiratory diseases

Cytokines are small, secreted proteins that control immune responses. Within the lung, they can control host responses to injuries or infection, resulting in clearance of the insult, repair of lung tissue, and return to homeostasis. Problems can arise when this response is over exuberant and/or cytokine production becomes dysregulated. In such cases, chronic and repeated inflammatory reactions and cytokine production can be established, leading to airway remodeling and fibrosis with unintended, maladaptive consequences. In this report, we describe the cytokines and molecular mechanisms behind the pathology observed in three major chronic diseases of the lung: asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis. Overlapping mechanisms are presented as potential sites for therapeutic intervention.

IL-18 induces airway hyperresponsiveness and pulmonary inflammation via CD4+ T cell and IL-13

IL-18 plays a key role in the pathogenesis of pulmonary inflammatory diseases including pulmonary infection, pulmonary fibrosis, lung injury and chronic obstructive pulmonary disease (COPD). However, it is unknown whether IL-18 plays any role in the pathogenesis of asthma. We hypothesized that overexpression of mature IL-18 protein in the lungs may exacerbate disease activities of asthma. We established lung-specific IL-18 transgenic mice on a Balb/c genetic background. Female mice sensitized– and challenged– with antigen (ovalbumin) were used as a mouse asthma model. Pulmonary inflammation and emphysema were not observed in the lungs of naïve transgenic mice. However, airway hyperresponsiveness and airway inflammatory cells accompanied with CD4⁺ T cells, CD8⁺ T cells, eosinophils, neutrophils, and macrophages were significantly increased in ovalbumin-sensitized and challenged transgenic mice, as compared to wild type Balb/c mice. We also demonstrate that IL-18 induces IFN-γ, IL-13, and eotaxin in the lungs of ovalbumin-sensitized and challenged transgenic mice along with an increase in IL-13 producing CD4⁺ T cells. Treatment with anti-CD4 monoclonal antibody or deletion of the IL-13 gene improves ovalbumin-induced airway hyperresponsiveness and reduces airway inflammatory cells in transgenic mice. Overexpressing the IL-18 protein in the lungs induces type 1 and type 2 cytokines and airway inflammation, and results in increasing airway hyperresponsiveness via CD4⁺ T cells and IL-13 in asthma.

Implications of Lymphocyte Anergy to Glycolipids in Multiple Sclerosis (MS): iNKT Cells May Mediate the MS Infectious Trigger

Immunogenic lipids may play key roles in host defenses against infection and in generating autoimmune inflammation and organ-specific damage. In multiple sclerosis (MS) there are unequivocal autoimmune features and vulnerability to aggravation or induction by microbial or viral infection. We have found glycolipid-driven anergy of circulating lymphocytes in MS indicating that this immune response is affected in MS and the robust effects of iNKT activation with potent cellular and cytokine activities emphasizes its potential importance. Diverse glycolipids including the endogenous myelin acetylated-galactosylceramides (AcGalCer) can drive activation that could be critical to the inflammatory demyelination in the central nervous system and clinical consequences. The iNKT cells and their invariant or iTCR (Vα24Jα18Vβ11) receptor an innate defense–a discrete immune arm that is separate from peptide-driven acquired immune responses. This offers new possibilities for insight including a likelihood that the pattern recognition of exogenous microbial and myelin immunogens can overlap and cross-react especially in an inflammatory milieu.

Association of interleukin-18 promoter polymorphisms with chronic obstructive pulmonary disease in male smokers

Chronic obstructive pulmonary disease (COPD) is considered a complex genetic disorder and it is expected that many genes play a role in the pathogenesis of this disease. Previous studies have reported that several variations within the interleukin (IL)-18 gene promoter region have been associated with different inflammatory diseases such as asthma. However, the association of IL-18 promoter polymorphisms with COPD has not been studied yet. We then performed a prospective case-control study to explore this association in male smokers of Chinese Han people. Our study recruited 112 COPD cases and 105 healthy controls matched for age. The genotyping of IL-18 promoter polymorphisms (-607 C/A and -137 G/C) was performed using TaqMan single nucleotide polymorphism genotyping assays. The frequencies of the alleles and genotypes in patients and controls were compared. We found that the frequency of IL-18 -607 C allele was significantly increased in patients with COPD (odds ratio (OR) = 1.48, 95% confidence interval (CI) = 1.01-2.15, P = 0.04). The frequency of IL-18 -607 C allele was significantly higher in the GOLD (Global initiative for Obstructive Lung Disease) 3-4 group compared with the GOLD 1-2 group (OR=2.06, 95% CI = 1.21-3.51, P = 0.01). There were no significant differences in the frequencies of the alleles and genotypes of IL-18 -137 G/C polymorphism between the patients and healthy smokers or between GOLD 3-4 group and GOLD 1-2 group. Our study revealed that the IL-18 -607 C/A polymorphism was associated with COPD susceptibility and severity of airflow limitation in male smokers of Chinese Han people.

Cross-roads in the lung: immune cells and tissue interactions as determinants of allergic asthma

Allergic asthma is a chronic disease of the lung characterized by underlying Th2- and IgE-mediated inflammation, structural alterations of the bronchial wall, and airway hyperresponsiveness. Initial allergic sensitization and later development of chronic disease are determined by close interactions between lung structural cells and the resident and migratory immune cells in the lung. Epithelial cells play a crucial role in allergic sensitization by directly influencing dendritic cells induction of tolerant or effector T cells and production of type 2 cytokines by innate immune cells. During chronic disease, the bronchial epithelium, stroma, and smooth muscle become structurally and functionally altered, contributing to the perpetuation of tissue remodeling. Thus, targeting tissue-driven pathology in addition to inflammation may increase the effectiveness of asthma treatment.

Characterization of IL-18 expression and release in the pathogenesis of chronic rhinosinusitis

BACKGROUND

Interleukin-18 (IL-18) is a member of the IL-1 cytokine family that affects chronic inflammation. We sought to characterize IL-18 expression and investigate its release during chronic rhinosinusitis (CRS).

METHODS

The expression of IL-18 in nasal polyps (NPs) and uncinate tissues (UTs) from both CRS and non-CRS patients was examined via immunohistochemistry. After culturing dispersed NP cells (DNPCs) with or without various stimulations, IL-18 levels were measured in the culture supernatants. Furthermore, the effect of IL-18 neutralization on staphylococcus enterotoxin B (SEB)-induced cytokine production was also examined.

RESULTS

Similar expression of IL-18 in the epithelial layers was observed between the NPs and UTs. However, there was a significantly higher number of IL-18(+) cells in the lamina propria from NPs compared to UTs without CRS. This increased number was significantly correlated with the radiological severity of sinusitis and local eosinophilia. After the dispersion, IL-18 was spontaneously released by NP cells in a phase-dependent manner. While SEB, fungal antigens, and TLR agonists did not enhance the release, exposure to protease or one cycle of a freeze-and-thaw treatment did induce release of IL-18 from rested DNPCs. In addition, neutralization of IL-18 significantly suppressed SEB-induced IL-5, IL-13, and IFN-γ, but not IL-17A production.

CONCLUSIONS

These results suggest that the pro-inflammatory effect of IL-18 released by danger signals may be involved in the pathogenesis of CRS, which includes eosinophilic inflammation and NP formation, via the augmentation of both Th2- and Th1-associated cytokine production.

The IL18 gene and Hashimoto thyroiditis in children

Interleukin 18 (IL18) stimulates interferon-γ production in Th1 cells which are prominent in the thyroid of Hashimoto thyroiditis (HT). We investigated the association between the IL18 gene and HT. There were 116 children with HT and 1272 controls. rs187238 and rs1946518 in the promoter region of the IL18 gene were genotyped. Differences in genotype, allele, carrier, and haplotype distributions between patients and controls were compared. A Pc value <0.05 was considered significant. The frequency of the C/G genotype of rs187238 was significantly higher in patients and conferred a risk of HT (OR, 1.96; 95% CI, 1.30-2.95; Pc, 0.0021). So did the frequencies of allele C (OR, 1.73; 95% CI, 1.22-2.44; Pc, 0.0035) and carrier C (OR, 1.96; 95% CI, 1.31-2.92; Pc, 0.0017), however the frequency of the G/G genotype was significantly lower in patients than in controls (OR, 0.51; 95% CI, 0.34-0.76; Pc, 0.0034). There was no association between HT and rs1946518. The CT haplotype was significantly more frequent in patients than in controls and conferred a risk of HT (OR, 1.76; 95% CI, 1.24-2.49; Pc, 0.0049). We concluded that the IL18 gene was associated with HT in children. The rs187238C allele and CT haplotype conferred a risk of HT.

Cytokines and cytokine-specific therapy in asthma

Asthma is increasing in prevalence worldwide. It is characterized by typical symptoms and variable airway obstruction punctuated with episodes of worsening symptoms known as exacerbations. Underlying this clinical expression of disease is airway inflammation and remodeling. Cytokines and their networks are implicated in the innate and adaptive immune responses driving airway inflammation in asthma and are modulated by host-environment interactions. Asthma is a complex heterogeneous disease, and the paradigm of Th2 cytokine-mediated eosinophilic inflammation as a consequence of allergic sensitization has been challenged and probably represents a subgroup of asthma. Indeed, as attention has switched to the importance of severe asthma, which represents the highest burden both to the patient and health care provider, there is an increasing recognition of inflammatory subphenotypes that are likely to be driven by different cytokine networks. Interestingly, these networks may be specific to aspects of clinical expression as well as inflammatory cell profiles and therefore present novel phenotype-specific therapeutic strategies. Here, we review the breadth of cytokines implicated in the pathogenesis of asthma and focus upon the outcomes of early clinical trials conducted using cytokines or cytokine-blocking therapies.

Interleukin-18 in pulmonary inflammatory diseases

The proinflammatory cytokine interleukin (IL)-18 was originally discovered as an interferon-γ-inducing factor in 1995. IL-18 is known to play an important role in Th1/Tc1 polarization and promoting the production of Th2 cytokines (e.g., IL-4, IL-5, IL-9, and IL-13) by T cells, NK cells, basophils, and mast cells. IL-18 can act as a cofactor for Th2 cell development and IgE production, and also plays an important role in the differentiation of Th17 cells. IL-18 is a key player in the pathogenesis of inflammatory diseases such as atopic dermatitis, rheumatoid arthritis, adult-onset Still's disease, Sjögren's syndrome, and inflammatory bowel diseases. Furthermore, many lines of evidence suggest that IL-18 plays a key role in the pathogenesis of pulmonary inflammatory diseases, including bronchial asthma and chronic obstructive pulmonary disease. Here, we review the pathological roles of IL-18 in pulmonary inflammatory diseases.

Pathogenesis of severe asthma

Patients with severe asthma have asthma symptoms which are difficult to control, require high dosages of medication, and continue to experience persistent symptoms, asthma exacerbations or airflow obstruction. Epidemiological and clinical evidences point to the fact that severe asthma is not a single phenotype. Cluster analyses have identified subclasses of severe asthma using parameters such as patient characteristics, and cytokine profiles have also been useful in classifying moderate and severe asthma. The IL-4/IL-13 signalling pathway accounts for the symptoms experienced by a subset of severe asthmatics with allergen-associated symptoms and high serum immunoglobulin E (IgE) levels, and these patients are generally responsive to anti-IgE treatment. The IL-5/IL-33 signalling pathway is likely to play a key role in the disease pathogenesis of those who are resistant to high doses of inhaled corticosteroid but responsive to systemic corticosteroids and anti-IL5 therapy. The IL-17 signalling pathway is thought to contribute to 'neutrophilic asthma'. Although traditionally viewed as players in the defence mechanism against viral and intracellular bacterial infection, mounting evidence supports a role for Th1 cytokines such as IL-18 and IFN-γ in severe asthma pathogenesis. Furthermore, these cytokine signalling pathways interact to contribute to the spectrum of clinical pathological outcomes in severe asthma. To date, glucocorticoids are the most effective anti-asthma drugs available, yet severe asthma patients are typically resistant to the effects of glucocorticoids. Glucocorticoid receptor dysfunction and histone deacetylase activity reduction are likely to contribute to glucocorticoid resistance in severe asthma patients. This review discusses recent development in different cytokine signalling pathways, their interactions and steroid resistance, in the context of severe asthma pathogenesis.

Novel identified receptors on mast cells

Mast cells (MC) are major participants in the allergic reaction. In addition they possess immunomodulatory roles in the innate and adaptive immune reactions. Their functions are modulated through a number of activating and inhibitory receptors expressed on their surface. This review deals with some of the most recently described receptors, their expression patterns, ligand(s), signal transduction mechanisms, possible cross-talk with other receptors and, last but not least, regulatory functions that the MC can perform based on their receptor expression in health or in disease. Where the receptor role on MC is still not clear, evidences from other hematopoietic cells expressing them is provided as a possible insight for their function on MC. Suggested strategies to modulate these receptors’ activity for the purpose of therapeutic intervention are also discussed.

Late increase of interleukin-18 levels in blood during Mycoplasma pneumoniae pneumonia

To the Editor, we read with great interest the article by Chung et al. which appeared recently in the journal. In that paper the authors reported that the decreased IL-18 response in severe pneumonia group vs. non-severe group was observed regardless of asthma status of the patients, whose findings were somewhat different from ours on non-asthmatic patients which showed higher serum levels of IL-18 in severe cases of pneumonia than in mild cases in terms of both in children and in adults. In this point, the timing of venous sampling must be an important factor in explaining the discrepant results. Our previous results suggest that the level of IL-18 in blood as a marker of disease severity should cautiously be interpreted considering a timing of sampling; a value of IL-18 in a blood sample which is obtained at the first visit to the hospital does not always represent the highest level of IL-18 because of the fact that the time which elapsed from the onset of illness to the blood sampling may vary among patients. Analyses on sequential samples, therefore, must be necessary to fully understand the perplexing nature of cytokine activation during Mycoplasma pneumoniae infection.

Effect of interleukin-18 gene polymorphisms on sensitization to wheat flour in bakery workers

Lower respiratory symptoms in bakery workers may be induced by wheat flour and endotoxins. We hypothesized that endotoxins from wheat flour may stimulate innate immunity and that interleukin-18 (IL-18) gene polymorphisms may affect their regulatory role in innate immune responses to endotoxins. To investigate the genetic contribution of IL-18 to sensitization to wheat flour, we performed a genetic association study of IL-18 in Korean bakery workers. A total of 373 bakery workers undertook a questionnaire regarding work-related symptoms. Skin prick tests with common and occupational allergens were performed and specific antibodies to wheat flour were measured by ELISA. Three polymorphisms of the IL-18 gene (-607A/C, -137G/C, 8674C/G) were genotyped, and the functional effects of the polymorphisms were analyzed using the luciferase reporter assay. Genotypes of -137G/C (GC or CC) and haplotype ht3 [ACC] showed a significant association with the rate of sensitization to wheat flour. Luciferase activity assay indicated ht3 [AC] as a low transcript haplotype. In conclusion, the regulatory role of IL-18 in lipopolysaccharide-induced responses in bakery workers may be affected by this polymorphism, thus contributing to the development of sensitization to wheat flour and work-related respiratory symptoms.

Inflammasome-regulated cytokines are critical mediators of acute lung injury

RATIONALE

Despite advances in clinical management, there are currently no reliable diagnostic and therapeutic targets for acute respiratory distress syndrome (ARDS). The inflammasome/caspase-1 pathway regulates the maturation and secretion of proinflammatory cytokines (e.g., IL-18). IL-18 is associated with injury in animal models of systemic inflammation.

OBJECTIVES

We sought to determine the contribution of the inflammasome pathway in experimental acute lung injury and human ARDS.

METHODS

We performed comprehensive gene expression profiling on peripheral blood from patients with critical illness. Gene expression changes were assessed using real-time polymerase chain reaction, and IL-18 levels were measured in the plasma of the critically ill patients. Wild-type mice or mice genetically deficient in IL-18 or caspase-1 were mechanically ventilated using moderate tidal volume (12 ml/kg). Lung injury parameters were assessed in lung tissue, serum, and bronchoalveolar lavage fluid.

MEASUREMENTS AND MAIN RESULTS

In mice, mechanical ventilation enhanced IL-18 levels in the lung, serum, and bronchoalveolar lavage fluid. IL-18-neutralizing antibody treatment, or genetic deletion of IL-18 or caspase-1, reduced lung injury in response to mechanical ventilation. In human patients with ARDS, inflammasome-related mRNA transcripts (CASP1, IL1B, and IL18) were increased in peripheral blood. In samples from four clinical centers, IL-18 was elevated in the plasma of patients with ARDS (sepsis or trauma-induced ARDS) and served as a novel biomarker of intensive care unit morbidity and mortality.

CONCLUSIONS

The inflammasome pathway and its downstream cytokines play critical roles in ARDS development.

Analysis of NLRP3 in the development of allergic airway disease in mice

The contribution of NLRP3, a member of the nucleotide-binding domain leucine-rich repeat-containing (NLR) family, to the development of allergic airway disease is currently controversial. In this study, we used multiple allergic asthma models to examine the physiologic role of NLRP3. We found no significant differences in airway eosinophilia, histopathologic condition, mucus production, and airway hyperresponsiveness between wild-type and Nlrp3(-/-) mice in either acute (alum-dependent) or chronic (alum-independent) OVA models. In addition to the OVA model, we did not detect a role for NLRP3 in the development of allergic airway disease induced by either acute or chronic house dust mite Ag exposure. Although we did not observe significant phenotypic differences in any of the models tested, we did note a significant reduction of IL-13 and IL-33 in Nlrp3(-/-) mice compared with wild-type controls in the chronic OVA model without added alum. In all of the allergic airway disease models, the NLRP3 inflammasome-associated cytokines IL-1β and IL-18 in the lung were below the level of detection. In sum, this report surveyed four different allergic asthma models and found a modest and selected role for NLRP3 in the alum-free OVA model. However, this difference did not greatly alter the clinical outcome of the disease. This finding suggests that the role of NLRP3 in allergic asthma must be re-evaluated.

Impact of interleukin-13 and -18 promoter polymorphisms in health care workers with natural rubber latex allergy

It is a matter of debate whether single nucleotide polymorphisms (SNP) in the promoter region of interleukin (IL)-13, an IgE regulator, and IL-18, an inducer of immune responses, modulating the respective protein expression, are accompanied by an increased risk of atopy, allergic asthma, and total IgE levels. The suspected associations were noted in health care workers (HCW) with and without latex allergy. IL-13 (-1055C>T) and three IL-18 (-656T>G, -607C>A, -137G>C) SNP were studied in 523 HCW with natural rubber latex (NRL) exposure and diagnosis in the late 1990s. Three hundred and thirty-four HCW displayed NRL sensitization and allergic symptoms, 93 with latex-allergic asthma, and 189 HCW with neither symptoms nor NRL sensitization. SNP analyses were performed by real-time polymerase chain reaction (PCR) using newly developed LightCycler assays. Analysis of IL-13 -1055C>T by analysis of variance (ANOVA) revealed significantly elevated total IgE levels in HCW carrying the CT or TT variant compared with the CC variant. None of the studied SNP showed an association with NRL-specific IgE. The IL-18 variants -656GG and -607CC displayed 99.5% linkage disequilibrium. Frequencies of alleles -656GG and -607CC were elevated in HCW with NRL asthma (48.4%) compared with HCW without symptoms (37.6%). In contrast, IL-18 -137G>C variants displayed an overall homogenous distribution. The association between the IL-13 -1055T allele and elevated total IgE levels confirms the role of a genetic background for total IgE regulation. The studied IL-18 SNP demonstrated no significant association with the clinical outcome, total IgE, or specific IgE in HCW with natural rubber latex allergy.

Relationship between single nucleotide polymorphism of interleukin-18 and susceptibility to pulmonary tuberculosis in the Chinese Han population

Interleukin-18 (IL-18) is a multi-functional cytokine capable of inducing either Th1 or Th2 polarization depending on the immunologic milieu. IL-18 may influence the host response to Mycobacterium tuberculosis (M.tb) infection. To investigate the relationship between single nucleotide polymorphisms of the IL-18 and susceptibility to pulmonary tuberculosis in the Chinese Han population, the IL-18 gene was sequenced to detect polymorphisms and to examine the genotype frequencies in 300 patients and 702 healthy controls. DNA sequencing revealed three IL-18 variants: rs1946518, rs5744247, and rs549908. It also revealed that allele A of rs1946518 confers a 1.47-fold increased risk of developing tuberculosis (TB) (P = 0.0001, OR [95%CI] = 1.47 [1.21-1.78]), and that the C allele of rs5744247 confers a 0.77-fold decreased risk of disease (P = 0.01, R [95%CI] = 0.77 [0.632-0.937]). The genotypes rs1946518, rs5744247 and rs549908 were found to be significantly associated with TB. Estimation of the frequencies of haplotypes revealed a potential risk haplotype AGA (P = 0.01, OR [95%CI] = 1.41 [1.15-1.72]) and a protective haplotype CCA (P = 0.01, OR [95%CI] = 0.70 [0.57-0.85]) for TB. The present findings suggest that polymorphisms in the IL-18 gene may affect susceptibility to TB and increase the risk of developing the disease in the Chinese Han population.

Common SNPs/haplotypes in IL18R1 and IL18 genes are associated with variations in humoral immunity to smallpox vaccination in Caucasians and African Americans

BACKGROUND

Identifying genetic factors that influence poxvirus immunity across races may assist in the development of better vaccines and approaches for vaccine development.

METHODS

We performed an extensive candidate-gene genetic screen (across 32 cytokine and cytokine receptor genes) in a racially diverse cohort of 1056 healthy adults after a single dose of smallpox vaccine. Associations between single-nucleotide polymorphisms (SNPs)/haplotypes and vaccinia virus-specific neutralizing antibodies were assessed using linear regression methodologies.

RESULTS

The combined analysis identified 63 associations between candidate SNPs and antibody levels after smallpox vaccination with P < .05. Thirty-one of these were within the IL18R1 and IL18 genes. Five IL18R1 SNPs, including a coding synonymous polymorphism rs1035130 (Phe251Phe) and 2 promoter SNPs (rs6710885, rs2287037), all in linkage disequilibrium, were associated with significant variations in antibody levels in both Caucasians (P ≤ .016) and African Americans (P ≤ .025). Similarly, associations with 2 intronic IL18 SNPs (rs2043055 and rs5744280) were consistent in the Caucasian (P ≤ .023) and African American samples (P ≤ .014). Haplotype analysis revealed highly significant associations between IL18R1 haplotypes and vaccinia virus-specific antibody levels (P < .001, by combined analysis) that were consistent across races.

CONCLUSIONS

Our study provides evidence for IL18 and IL18R1 genes as plausible genes regulating the humoral immune response to smallpox vaccine in both Caucasians and African Americans.