Role of IL‐17 in atopy—A systematic review

Purpose of Review Atopy is defined as the genetic predisposition to react with type I allergic diseases such as food‐, skin‐, and respiratory allergies. Distinct molecular mechanisms have been described, including the known Th2 driven immune response. IL‐17A (IL‐17) is mainly produced by Th17 cells and belongs to the IL‐17 family of cytokines, IL‐17A to F. While IL‐17 plays a major role in inflammatory and autoimmune disorders, more data was published in recent years elucidating the role of IL‐17 in allergic diseases. The present study aimed to elaborate specifically the role of IL‐17 in atopy. Methods A systematic literature search was conducted in MEDLINE, Embase, and Cochrane Central Register of Controlled Trials, regarding IL‐17 and atopy/allergic diseases. Results In total, 31 novel publications could be identified (food allergy n = 3, allergic asthma n = 7, allergic rhinitis [AR] n = 10, atopic dermatitis [AD] n = 11). In all allergic diseases, the IL‐17 pathway has been investigated. Serum IL‐17 was elevated in all allergic diseases. In AR, serum and nasal IL‐17 levels correlated with the severity of the disease. In food allergies, serum IL‐17E was also elevated in children. In AD, there is a trend for higher IL‐17 values in the serum and skin specimen, while it is more expressed in acute lesions. In allergic asthma, serum IL‐17 levels were increased. In two studies, higher serum IL‐17 levels were found in severe persistent asthmatic patients than in intermittent asthmatics or healthy controls. Only one therapeutic clinical study exists on allergic diseases (asthma patients) using a monoclonal antibody against the IL‐17 receptor A. No clinical efficacy was found in the total study population, except for a subgroup of patients with (post‐bronchodilator) high reversibility. Summary The role of IL 17 in the pathogenesis of allergic diseases is evident, but the involvement of the Th17 cytokine in the pathophysiological pathway is not conclusively defined. IL‐17 is most likely relevant and will be a clinical target in subgroups of patients. The current data indicates that IL‐17 is elevated more often in acute and severe forms of allergic diseases.