IL-22 promotes allergic airway inflammation in epicutaneously sensitized mice

Abstract

Background: Serum IL-22 levels are increased in patients with atopic dermatitis, which commonly precedes asthma in the atopic march. Epicutaneous sensitization in mice results in T_H2-dominated skin inflammation that mimics atopic dermatitis and sensitizes the airways for antigen challenge-induced allergic inflammation characterized by the presence of both eosinophils and neutrophils. Epicutaneous sensitization results in increased serum levels of IL-22.

Objective: We sought to determine the role of IL-22 in antigen-driven airway allergic inflammation after inhalation challenge in epicutaneously sensitized mice.

Methods: Wild-type (WT) and Il22^-/- mice were sensitized epicutaneously or immunized intraperitoneally with ovalbumin (OVA) and challenged intranasally with antigen. OVA T-cell receptor-specific T cells were T_H22 polarized in vitro. Airway inflammation, mRNA levels in the lungs, and airway hyperresponsiveness (AHR) were examined.

Results: Epicutaneous sensitization preferentially elicited an IL-22 response compared with intraperitoneal immunization. Intranasal challenge of mice epicutaneously sensitized with OVA elicited in the lungs Il22 mRNA expression, IL-22 production, and accumulation of CD3⁺CD4⁺IL-22⁺ T cells that coexpressed IL-17A and TNF-α. Epicutaneously sensitized Il22^-/- mice exhibited diminished eosinophil and neutrophil airway infiltration and decreased AHR after intranasal OVA challenge. Production of IL-13, IL-17A, and TNF-α was normal, but IFN-γ production was increased in lung cells from airway-challenged and epicutaneously sensitized Il22^-/- mice. Intranasal instillation of IFN-γ-neutralizing antibody partially reversed the defect in eosinophil recruitment. WT recipients of T_H22-polarized WT, but not IL-22-deficient, T-cell receptor OVA-specific T cells, which secrete both IL-17A and TNF-α, had neutrophil-dominated airway inflammation and AHR on intranasal OVA challenge. Intranasal instillation of IL-22 with TNF-α, but not IL-17A, elicited neutrophil-dominated airway inflammation and AHR in WT mice, suggesting that loss of IL-22 synergy with TNF-α contributed to defective recruitment of neutrophils into the airways of Il22^-/- mice. TNF-α, but not IL-22, blockade at the time of antigen inhalation challenge inhibited airway inflammation in epicutaneously sensitized mice.

Conclusion: Epicutaneous sensitization promotes generation of antigen-specific IL-22-producing T cells that promote airway inflammation and AHR after antigen challenge, suggesting that IL-22 plays an important role in the atopic march.

Keywords: IL-22; asthma; atopic dermatitis; neutrophils.