Interleukin-26 is associated with the level of systemic inflammation and lung functions in obese and non-obese moderate-to-severe asthmatic patients.

Introduction: Obese asthma is a complex syndrome, which includes different phenotypes of disease. At present, these phenotypes only have started to acquire a sufficient understanding. It was suggested that IL-26 is a potential biomarker of disease severity in asthma without signs of Th2-mediated inflammation. In this study, we investigated the serum and exhaled levels of IL-26 and its associations with the level of systemic inflammation, lung functions, and body weight in obese and non-obese moderate-to-severe asthmatic patients MATERIAL AND METHODS: The study included 10 healthy subjects, 10 obese subjects without lung pathologies, 10 non-obese asthmatics (NOA) (BMI 18.5-24.9 kg/m²), and 40 obese asthmatics (OA) (BMI 25.0-49.9 kg/m²). During the visit, patients' examination and spirometry with the bronchodilator reversibility test were conducted, the exhaled breath condensate (EBC) was obtained, and the blood samples were collected. The level of IL-26, interleukin-1β (IL-1β), interleukin-4 (IL-4), interleukin-6 (IL-6), TNF-α, interleukin-10 (IL-10), total and specific immunoglobulin E (IgE), and high sensitive C reactive protein (hs-CRP) were measured using the ELISA kits. Statistical comparison between 2 groups was analyzed using the Mann-Whitney rank-sum test. Chi-square with Yates' correction was used to compare frequencies. Spearman's rank test was used for correlating nonparametric variables. The Receiver Operating Characteristic (ROC) curve and the area under ROC curve (AUC) were used for evaluating the diagnostic power of IL-26 as a possible biomarker.

Results: NOA had a reversible airway obstruction with reduced FEV1, FEV1/FVC, FVC 25/75, and positive post-bronchodilator test (PBT), significantly increased serum levels of IL-10, IL-4, and slightly increased IL-26. NOA had significantly increased exhaled IL-26 in comparison with healthy subjects. The obese subjects had a normal ventilatory pattern without airway obstruction, and differences in serum IL-26, IL-10, and IL-4 concentrations in comparison with healthy subjects. Obese subjects had a significant escalation of hs-CRP and no differences in the levels of exhaled IL-26, IL-10, and hs-CRP as compared with healthy subjects. OA had reduced FEV1, FEV1/FVC, and FEV25-75 in comparison with non-obese asthmatics. OA had elevated IL-26, IL-10, IL-4, and hs-CRP concentrations as compared with healthy subjects. These patients had a partial similarity with both non-obese asthmatics (elevated IL-26, IL-10, and IL-4) and obese subjects (elevated, IL-1β, IL-6, TNF-α, hs-CRP). OA had a reduced concentration of exhaled IL-26 in comparison with NOA and elevated exhaled IL-10 in comparison with obese subjects. Furthermore, OA had an increased concentration of IL-1β and TNF-α in comparison with healthy individuals and NOA. Exhaled IL-26 concentration distinguished non-obese asthmatics from healthy subjects, asthmatic patients from non-asthmatics (healthy and obese subjects), all asthmatic patients from non-asthmatics (healthy and obese subjects).

Conclusions: Exhaled IL-26 elevated in obese and non-obese moderate-to-severe asthmatic patients. Exhaled IL-26 might be a perspective biomarker in non-obese and obese asthmatics. The obese asthmatic phenotype comprised the combined systemic and local airway inflammation.