Analysis of helper T cell subset in severe asthma for the development of new immunotherapy

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Asthma is chronic airway inflammation characterized by eosinophil infiltration, mucus hypersecretion, and airway hyperresponsiveness (AHR) to a variety of stimuli. These characteristics are mainly mediated by antigen-specific Th2 cells and their cytokines including IL-4, IL-5, and IL-13. Moreover, we and others have shown that Th17 cells induce neutrophilc airway inflammation in part through the production of IL-17A. More recently, IL-22, one of Th17 cell-derived cytokines with both proinflammatory and anti-inflammatory properties, has been shown to be detected in the airways in a murine model of asthma. However, the role of IL-22 in the regulation of allergic airway inflammation remains largely unknown.In this study, we found that IL-22 was produced by CD4^+ T cells infiltrating in the airways upon antigen challenge, that the neutralization of IL-22 by anti-IL-22 antibody in the effector phase enhanced antigen-induced eosinophil recruitment into the airways, and that intranasal administration of recombinant IL-22 inhibited antigen-induced eosinophil recruitment into the airways. We also found that anti-IL-22 antibody enhanced antigen-induced IL-25 production in the airways, which is known to enhance Th2-type immune responses in the airways, and indeed co-injection of anti-IL-25 antibody reversed the enhancing effect of anti-IL-22 antibody on antigen-induced eosinophil recruitment into the airways. Finally, we found that IL-22 inhibited IL-13-mediated enhancement of IL-25 expression in LPS-stimulated lung epithelial cell line MLE-15 cells. Our results suggest that IL-22 attenuates antigen-induced airway inflammation in part by inhibiting the expression of IL-25 in lung epithelial cells.