Interleukin-26 in host defense and inflammatory disorders of the airways

Systemic IL-26 correlates with improved asthma control in children sensitized to dog allergen

BACKGROUND

Interleukin (IL)-26 is produced by T helper type 17 (Type 17) cells and exerts immunomodulatory plus antimicrobial effects. Previous studies show that local IL-26 concentrations in the airways are higher in patients with uncontrolled than in those with controlled asthma, and that this intriguing cytokine bears biomarker potential. Here, we determined how systemic IL-26 relates to allergen sensitization, asthma severity, and to IL-17 A in children.

METHODS

Serum samples were obtained from children with (n = 60) and without (n = 17) sensitization to dog allergen, and IL-26 and IL-17 A protein concentrations were measured using ELISA. Self-reported history, including medication use and validated symptom-based questionnaire scores, was recorded.

RESULTS

The serum concentrations of IL-26 were enhanced in allergen-sensitized subjects and correlated with those of IL-17 A in a positive manner. However, the IL-26 concentrations did not markedly differ between allergen-sensitized subjects with and without asthma, eczema, allergic rhinitis, or a history of food allergy. Notably, IL-26 concentrations correlated with increasing Asthma Control Test (ACT) scores in a positive manner and with inhaled corticosteroid in a negative manner, amongst sensitized subjects with asthma. Moreover, subjects with asthma requiring ≥ 1 course of oral corticosteroids in the preceding 12 months had decreased IL-26 concentrations.

CONCLUSION

This study forwards evidence that systemic IL-26, just like IL-17 A, is involved in allergen sensitization among children. The association of systemic IL-26 with improved asthma control is compatible with the cellular sources being recruited into the airways in severe asthma, which supports that this kinocidin bears potential as a biomarker and therapeutic target.

Involvement of IL-26 in bronchiolitis obliterans syndrome but not in acute rejection after lung transplantation

BACKGROUND

 The main long-term complication after lung transplantation is bronchiolitis obliterans syndrome (BOS), a deadly condition in which neutrophils may play a critical pathophysiological role. Recent studies show that the cytokine interleukin IL-26 can facilitate neutrophil recruitment in response to pro-inflammatory stimuli in the airways. In this pilot study, we characterized the local involvement of IL-26 during BOS and acute rejection (AR) in human patients.

METHOD

 From a biobank containing bronchoalveolar lavage (BAL) samples from 148 lung transplant recipients (LTR), clinically-matched patient pairs were identified to minimize the influence of clinical confounders. We identified ten pairs (BOS/non-BOS) with BAL samples harvested on three occasions for our longitudinal investigation and 12 pairs of patients with and without AR. The pairs were matched for age, gender, preoperative diagnosis, type of and time after surgery. Extracellular IL-26 protein was quantified in cell-free BAL samples using an enzyme-linked immunosorbent assay. Intracellular IL-26 protein in BAL cells was determined using immunocytochemistry (ICC) and flow cytometry.

RESULTS

 The median extracellular concentration of IL-26 protein was markedly increased in BAL samples from patients with BOS (p < 0.0001) but not in samples from patients with AR. Intracellular IL-26 protein was confirmed in alveolar macrophages and lymphocytes (through ICC and flow cytometry) among BAL cells obtained from BOS patients.

CONCLUSIONS

 Local IL-26 seems to be involved in BOS but not AR, and macrophages as well as lymphocytes constitute cellular sources in this clinical setting. The enhancement of extracellular IL-26 protein in LTRs with BOS warrants further investigation of its potential as a target for diagnosing, monitoring, and treating BOS.

IL-26 in asthma and COPD

INTRODUCTION

New targets are needed to enable more accurate diagnosis, monitoring and effective therapy in uncontrolled asthma and chronic obstructive pulmonary disease (COPD), two disorders characterized by pathogenic alterations in the innate immune response. Interestingly, the IL-10-related cytokine IL-26 has been found to be abundantly expressed in human airways and alterations in its expression have been linked to reduced lung function and markers of neutrophilic inflammation in patients with uncontrolled asthma or COPD.

AREAS COVERED

Literature search was conducted on PubMed to identify articles in the field of IL-26 immunology, as well as clinical studies on IL-26 in asthma and COPD, published between 2000 and 2021. We outline the main sources of IL-26 in human airways, as well as the effect of this cytokine on relevant immune and structural cells. Finally, we discuss the potential involvement of IL-26 in the pathophysiology of uncontrolled asthma and COPD.

EXPERT OPINION

IL-26 constitutes a potential target for diagnostic purposes and therapeutic modulation of the innate immune response in the airways of patients with asthma and COPD. It seems reasonable to expect more conclusive evidence of its clinical utility for personalized medicine within the coming 5-year period.

Complex Involvement of Interleukin-26 in Bacterial Lung Infection

Pneumonia is a global cause of mortality, and this provides a strong incentive to improve the mechanistic understanding of innate immune responses in the lungs. Here, we characterized the involvement of the cytokine interleukin (IL)-26 in bacterial lung infection. We observed markedly increased concentrations of IL-26 in lower airway samples from patients with bacterial pneumonia and these correlated with blood neutrophil concentrations. Moreover, pathogen-associated molecular patterns (PAMPs) from both Gram-negative and -positive bacteria increased extracellular IL-26 concentrations in conditioned media from human models of alveolar epithelial cells, macrophages, and neutrophils in vitro. Stimulation with IL-26 inhibited the inherent release of neutrophil elastase and myeloperoxidase in unexposed neutrophils. This stimulation also inhibited the expression of activity makers in neutrophils exposed to Klebsiella pneumoniae. In addition, priming of human lung tissue ex vivo with exogenous IL-26 potentiated the endotoxin-induced increase in mRNA for other cytokines involved in the innate immune response, including the master Th17-regulator IL-23 and the archetype inhibitory cytokine IL-10. Finally, neutralization of endogenous IL-26 clearly increased the growth of Klebsiella pneumoniae in the macrophage culture. These findings suggest that IL-26 is involved in bacterial lung infection in a complex manner, by modulating critical aspects of innate immune responses locally and systemically in a seemingly purposeful manner and by contributing to the killing of bacteria in a way that resembles an antimicrobial peptide. Thus, IL-26 displays both diagnostic and therapeutic potential in pneumonia and deserves to be further evaluated in these respects.