Increased serum IL-17A and Th2 cytokine levels in patients with severe uncontrolled asthma

Asthma is a syndrome of chronic bronchial inflammation and airway remodelling. Initially, asthma has been categorized into atopic and nonatopic types, based on antigen-specific IgE levels. Moreover, recently, asthma has been classified into different endotypes based on its pathophysiology, leading to the selection of the most optimal and effective therapies. Although T helper cell type 2 (Th2) cytokines were proven to play critical roles in atopic asthma, IL-17A has been reported to be involved in severe refractory asthma. Patients and methods: In this study, we measured the levels of 24 cytokines/chemokines in the sera of healthy controls (HCs) (n = 34) and patients with asthma (n = 77), that were compared among patient groups with different disease activities and characteristics. Results: The serum levels of nine cytokines were significantly higher in patients with asthma than in HCs, and the levels of IL-17A and SCF were significantly different between uncontrolled and well-controlled patient groups (p = 0.003). The IL-17A levels were significantly correlated with those of IL-4, IL-25, IL-10, and IFN-gamma in patients with uncontrolled asthma, and the patients with the highest levels of all the above cytokines were refractory to high-dose of inhaled corticosteroid therapy and have a history of acute exacerbation within 1 year, requiring systemic steroid therapy. Discussion: This study examines the profiles of upregulation and downregulation of various cytokines and chemokines in relation to asthmatic control status. IL-17A was significantly upregulated in patients with the uncontrolled and refractory status. Therefore, IL-17A may play important roles in asthmatic exacerbation, and its high level, in combination with upregulated Th2 and other cytokines, may indicate the refractory endotype of asthma.