Bringing in the cavalry: IL-26 mediates neutrophil recruitment to the lungs

The Association of Toll-like Receptor-9 Gene Single-Nucleotide Polymorphism and AK155(IL-26) Serum Levels with Chronic Obstructive Pulmonary Disease Exacerbation Risk: A Case-Controlled Study with Bioinformatics Analysis

Background: A crucial challenge is the determination of chronic obstructive pulmonary disease (COPD) immune-related mechanisms, where one of the important components of the inflammatory axes in COPD is Toll-like receptor-9 (TLR9) and interleukin-26 AK155(IL-26). Aim: To examine the relation between TLR9 (T1237C) SNP rs5743836 and serum levels of AK155(IL-26) with the exacerbation of COPD. Subjects: A total of 96 COPD patients sub-classified into two groups. Materials: DNA was purified from blood samples of stable COPD patients (n = 48) vs. exacerbated COPD patients (n = 48) as well as 42 age- and sex-matched healthy smokers and passive smokers as a control group. Methods: Genotyping for TLR9 rs5743836 (T1237C) polymorphism was performed using real time polymerase chain reaction (RT-PCR). AK155(IL-26) serum levels were determined using ELISA. Results: There is a significantly higher frequency of the mutant homozygous genotype (C/C) and the mutated C allele of TLR9 rs5743836 (T1237C) in COPD patients and in the exacerbated group when compared with the control group and stable COPD patients, respectively, with OR 31.98, 1.8 to 57.7, and OR 3.64, 0.98 to 13.36, respectively. For the mutated C allele, the OR was 3.57, 1.94 to 6.56, p = 0.001, OR 1.83, 1.02 to 3.27, p = 0.041, respectively. In the exacerbated COPD group, there was a significant association between TLR9 rs5743836 SNP and BMI and the lung vital function measures, CRP, and AK155(IL-26). The exacerbated COPD group has higher serum levels of AK155(IL-26) compared with the stable group or when compared with the control group (p = 0.001) for both. AK155(IL-26) serum levels have a positive significant correlation with CRP and BMI and a significant negative correlation with FEV1% and FEV1/FVC in exacerbated COPD patients. Conclusions: Our results demonstrated a relation linking TLR-9 rs5743836 (T1237C) expression and the risk of COPD development and its exacerbation, indicating that dysfunctional polymorphisms of the innate immune genes can affect COPD development and its exacerbation. AK155(IL-26) upregulation was related to decreased lung functionality, systematic inflammatory disease, and COPD exacerbation.

IL-26 in the Lung and Its Role in COPD Inflammation

IL-26 is a cytokine expressed by infiltrating pro-inflammatory IL-17-producing T cells in the tissues of patients with chronic lung inflammation. IL-26 induces the chemotactic response of human neutrophils to bacteria and other inflammatory stimuli. In recent years, the innovative properties of IL-26 have been described. Studies have shown that, as DNA is released from damaged cells, it binds to IL-26, which plays the role of a carrier molecule for extracellular DNA, further contributing to its binding to the site of inflammation. This mechanism of action indicates that IL-26 may serve both as a driver as well as a stimulus of the inflammatory process, leading to the installation of a noxious amplification loop and, eventually, persistent inflammation. IL-26 also demonstrates direct antimicrobial effects derived from its capability to create pores and disrupt bacterial membranes, as indicated by the presence of membrane blebs on the surface of the bacteria and cytosolic leakage pores in bacterial walls, produced in response to microbial stimuli in human airways by several different immune and structural cells. Surprisingly, while this particular cytokine induces the gathering of neutrophils in areas of infection, it also exhibits inhibitory and pro-inflammatory effects on airway epithelial and immune cells. These remarkable effects underline the necessity of a better understating of its biological behavior and its role in the pathophysiology and disease burden in several smoking-related airway inflammatory disorders, such as Chronic Obstructive Pulmonary Disease (COPD) and chronic bronchitis. In this review, we aim to discuss the current role of IL-26 in the lung, with an emphasis on systemic inflammation in patients suffering from COPD and chronic bronchitis.

IL-26 gene variants and protein expression in Tunisian asthmatic patients

The interleukin-26 (IL-26), a member of the IL-10 family is one of the latest discovered cytokines which contributes in numerous chronic autoimmune and inflammatory disorders. In the current case-control study, we investigated the distribution of three IL-26 single nucleotide polymorphisms (SNPs) (rs7134599, rs2870946 & rs1558744) in 440 Tunisian adults via Taqman genotyping assay. The presence of rs7134599 and rs1558744 polymorphisms considerably reduced the risk of developing asthma while the rs7134599 AA [OR = 0.40, CI: 0.23-0.70] and AG [OR = 0.50, CI (0.32-0.76)] genotypes protected against the asthma risk. The rs7134599 A allele was correlated with a lower risk of developing severe asthma (p < 0.001) while that of the rs2870946 CC genotype was associated with a higher risk of developing asthma in smoking patients (p < 0.001). In addition, we measured the IL-26 levels in the serum by an Enzyme-linked-Immunosorbent Assay (ELISA). During the analysis, we found that IL-26 serum levels were incredibly increased in asthmatic patients compared to the healthy controls. Our study revealed a significant association of IL-26 gene polymorphisms with asthma for the first time which can serve as biomarkers for asthma in the Tunisian population. The significant increase of IL-26 serum protein levels in asthma patients suggested a major role of IL-26 in asthma phenotypes.

Sputum IL-26 Is Overexpressed in Severe Asthma and Induces Proinflammatory Cytokine Production and Th17 Cell Generation: A Case-Control Study of Women

Objective

Asthma inflammation is a complex pathway involving numerous mediators. Interleukin-26 (IL-26), a member of the IL-10 cytokine family, is abundant in human airways and induces the production of proinflammatory cytokines. Our aim was to investigate the possible role of IL-26 in severe asthma. We analysed the expression of IL-26 in severe asthma both in peripheral blood and induced sputum.

Patients and Methods

A total of 50 adult women with severe asthma were recruited and compared to 30 healthy controls (HC). Serum and sputum fluid (SF) levels of IL-26 and IL-17 were defined by ELISA. IL-26 mRNA expression and IL-26 protein were analysed using RT-PCR and Western blot. In vitro, we studied the effect of recombinant IL-26 (rIL-26) and SF-IL-26 on cultured CD4⁺ T cells and monocytes, comparing patients and controls.

Results

Concentrations of IL-26 are higher in serum and induced sputum of asthmatic patients than in HC. Moreover, IL-26 protein and mRNA expression were significantly elevated in asthma sputum cells compared to PBMCs. We observed a positive correlation between body mass index (BMI) and sputum fluid IL-26, while the correlation between IL-26 and lung function tests (FEV1% and FEV1/FVC ratio) was negative. IL-17A was highly expressed in SF and correlated positively with IL-26. In patients’ sputum IL-26 and IL-17A were significantly associated with neutrophils. Stimulation of cultured CD4⁺ T cells with monocytes by recombinant IL-26 promoted the generation of RORγt⁺ Th17⁺ cells inducing the production of IL-17A, IL-1β, IL-6 and TNF-α cytokines. IL-26 expressed in SF was biologically active and induced IL-17 secretion in the presence of IL-1β and IL-6 cytokines.

Conclusion

These findings show that IL-26 is highly produced in asthmatic sputum, induces pro-inflammatory cytokine secretion by monocytes/macrophages, and favours Th17 cell generation. IL-26 thereby appears as a novel pro-inflammatory cytokine, produced locally in the airways that may constitute a promising target to treat asthma inflammatory process.

The neutrophil-mobilizing cytokine interleukin-26 in the airways of long-term tobacco smokers

Long-term tobacco smokers with chronic obstructive pulmonary disease (COPD) or chronic bronchitis display an excessive accumulation of neutrophils in the airways; an inflammation that responds poorly to established therapy. Thus, there is a need to identify new molecular targets for the development of effective therapy. Here, we hypothesized that the neutrophil-mobilizing cytokine interleukin (IL)-26 (IL-26) is involved in airway inflammation amongst long-term tobacco smokers with or without COPD, chronic bronchitis or colonization by pathogenic bacteria. By analyzing bronchoalveolar lavage (BAL), bronchail wash (BW) and induced sputum (IS) samples, we found increased extracellular IL-26 protein in the airways of long-term smokers in vivo without further increase amongst those with clinically stable COPD. In human alveolar macrophages (AM) in vitro, the exposure to water-soluble tobacco smoke components (WTC) enhanced IL-26 gene and protein. In this cell model, the same exposure increased gene expression of the IL-26 receptor complex (IL10R2 and IL20R1) and nuclear factor κ B (NF-κB); a proven regulator of IL-26 production. In the same cell model, recombinant human IL-26 in vitro caused a concentration-dependent increase in the gene expression of NF-κB and several pro-inflammatory cytokines. In the long-term smokers, we also observed that extracellular IL-26 protein in BAL samples correlates with measures of lung function, tobacco load, and several markers of neutrophil accumulation. Extracellular IL-26 was further increased in long-term smokers with exacerbations of COPD (IS samples), with chronic bronchitis (BAL samples ) or with colonization by pathogenic bacteria (IS and BW samples). Thus, IL-26 in the airways emerges as a promising target for improving the understanding of the pathogenic mechanisms behind several pulmonary morbidities in long-term tobacco smokers.

Interleukin-26 Production in Human Primary Bronchial Epithelial Cells in Response to Viral Stimulation: Modulation by Th17 cytokines

Interleukin (IL)-26 is abundant in human airways and this cytokine is involved in the local immune response to a bacterial stimulus in vivo. Specifically, local exposure to the toll-like receptor (TLR) 4 agonist endotoxin does increase IL-26 in human airways and this cytokine potentiates chemotactic responses in human neutrophils. In addition to T-helper (Th) 17 cells, alveolar macrophages can produce IL-26, but it remains unknown whether this cytokine can also be produced in the airway mucosa per se in response to a viral stimulus. Here, we evaluated whether this is the case using primary bronchial epithelial cells from the airway epithelium in vitro, and exploring the signaling mechanisms involved, including the modulatory effects of additional Th17 cytokines. Finally, we assessed IL-26 and its archetype signaling responses in healthy human airways in vivo. We found increased transcription and release of IL-26 protein after stimulation with the viral-related double stranded (ds) RNA polyinosinic-polycytidylic acid (poly-IC) and showed that this IL-26 release involved mitogen-activated protein (MAP) kinases and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). The release of IL-26 in response to a viral stimulus was modulated by additional Th17 cytokines. Moreover, there was transcription of IL26 mRNA and expression of the protein in epithelial cells of bronchial brush and tissue biopsies respectively after harvest in vivo. In addition, the extracellular IL-26 protein concentrations in bronchoalveolar lavage (BAL) samples did correlate with increased epithelial cell transcription of an archetype intracellular signaling molecule downstream of the IL-26-receptor complex, STAT1, in the bronchial brush biopsies. Thus, our study suggests that viral stimulation causes the production of IL-26 in lining epithelial cells of human airway structural cells that constitute a critical immune barrier and that this production is modulated by Th17 cytokines.

Interleukin-26 is overexpressed in Behçet's disease and enhances Th17 related -cytokines

Behçet's disease (BD) is a multi-systemic inflammatory disorder characterized by the "triple symptom complex". Several pro-inflammatory cytokines, mainly derived from the immune Th17 axis, seem to be involved in different pathogenic pathways leading to development of the clinical manifestations. Here, we have analyzed the expression and role of IL-26 in active BD patients, an inflammatory disorder characterized by bronchoalveolar lavage fluid (BAL) and cerebrospinal fluid (CSF) inflammation. On this basis, the primary aim of our work was to study IL-26 levels in serum, BAL CSF) from active BD patients. Samples were collected from 95 BD patients (55 patients were in active stage) and 50 healthy controls (HC). They were investigated with ELISA for estimation of cytokines levels. Serum concentration of IL-26 resulted higher in both active [4.80±1.32] and inactive [2.77±1.026] BD than HC [0.31±0.14ng/ml; p<0.0001]. Level of IL-26 was associated with the BD clinical severity score from moderate to severe (P<0.0001). IL-26 was highly expressed in CSF [10.80±2.05ng/ml] and in BAL [12.89±3.03ng/ml] fluid from BD patients comparatively to their respective controls. IL-26 levels in CSF and in BAL fluid showed positive correlations with IL-17 level and an inversely correlation with IL-37. Interestingly, IL-26-stimulated CD4⁺ T cells and monocytes promote the generation of Th17 (IL-17A, IL-23) and suppress Treg (IL-10, TGF-β) cytokines. Our findings may suggest a signature of IL-26 probably responsible for the inflammatory process to correlate positively with Th17 cytokines and inversely with Treg mediators. This evidence could contribute to improve the knowledge regarding the role of IL-26 in BD severity. For the first time, IL-26 expression is demonstrated in BAL and CSF, supporting a role for this cytokine in the pathogenesis of BD. IL-26 thereby appears as a novel proinflammatory cytokine favoring the generation of Th17 cytokines.

The cytokine interleukin-26 as a biomarker in pediatric asthma

In this pilot study, we examined associations between local interleukin (IL)-26, disease severity and biomarkers of Th2-mediated inflammation in a well-defined cohort of pediatric patients (14 years median age, 41 % females) with controlled (n = 28) or uncontrolled (n = 48) asthma. Sputum IL-26 protein concentrations (ELISA) reflected disease control in patients without local (low exhaled nitric oxide) or systemic (low blood eosinophils) signs of eosinophilic inflammation. Moreover, sputum-IL-26 concentrations correlated with those of blood neutrophils. Our study indicates that IL-26 is a potential biomarker of disease severity in pediatric asthma without signs of Th2-mediated inflammation.