IL-25 enhances allergic airway inflammation by amplifying a TH2 cell–dependent pathway in mice

BackgroundA novel IL-17 family cytokine, IL-25, has been reported to induce IL-4, IL-5, and IL-13 production from undefined non-T/non-B cells and then induce TH2-type immune responses. However, the roles of IL-25 in inducing allergic airway inflammation remain unknown.ObjectiveWe sought to determine whether IL-25 is involved in causing allergic airway inflammation.MethodsWe examined the expression of IL-25 mRNA in the lungs of sensitized mice on antigen inhalation. We also examined the effect of IL-25 neutralization by soluble IL-25 receptor on antigen-induced airway inflammation. We then generated IL-25 transgenic mice that express IL-25 specifically in the lung under the control of the Clara cells–10-kd protein promoter and investigated the effect of enforced IL-25 expression on antigen-induced airway inflammation.ResultsIL-25 mRNA was expressed in the lungs of sensitized mice on antigen inhalation, and the neutralization of IL-25 by soluble IL-25 receptor decreased antigen-induced eosinophil and CD4+ T-cell recruitment into the airways. The enforced expression of IL-25 in the lung itself failed to induce allergic airway inflammation, whereas the expression of IL-25 significantly enhanced antigen-induced TH2 cytokine production, eosinophil and CD4+ T cell recruitment, and goblet cell hyperplasia in the airways. Moreover, IL-25–induced enhancement of allergic airway inflammation was inhibited by the depletion of CD4+ T cells or by the absence of signal transducer and activator of transcription 6.ConclusionIL-25 enhances antigen-induced allergic airway inflammation by amplifying a TH2 cell–dependent pathway.Clinical implicationsIL-25 might be involved in the enhancement, prolongation, or both of TH2 cell–mediated allergic diseases, such as asthma.