IL-33 dysregulates regulatory T cells and impairs established immunologic tolerance in the lungs.

BACKGROUND: Airway exposure to environmental antigens generally leads to immunologic tolerance. A fundamental question remains: Why is airway tolerance compromised in patients with allergic airway diseases? IL-33 promotes innate and adaptive type 2 immunity and might provide the answer to this question.
OBJECTIVE: The goal of this study was to investigate the roles played by IL-33 in altering regulatory T (Treg) cells in the lungs and in affecting previously established airway immunologic tolerance.
METHODS: We analyzed CD4+ forkhead box P3 (Foxp3)+ Treg cells that were isolated from the lungs of naive BALB/c mice and those treated with IL-33. Airway tolerance and allergen-induced airway inflammation models in mice were used to investigate how IL-33 affects established immunologic tolerance in vivo.
RESULTS: CD4+Foxp3+ Treg cells in the lungs expressed the IL-33 receptor ST2. When exposed to IL-33, Treg cells upregulated their expression of the canonical TH2 transcription factor GATA3, as well as ST2, and produced type 2 cytokines. Treg cells lost their ability to suppress effector T cells in the presence of IL-33. Airway administration of IL-33 with an antigen impaired immunologic tolerance in the lungs that had been established by prior exposure to the antigen. Dysregulated Foxp3+ Treg cells with distinct characteristics of TH2 cells increased in the lungs of mice undergoing IL-33-dependent allergen-driven airway inflammation.
CONCLUSIONS: IL-33 dysregulated lung Treg cells and impaired immunologic tolerance to inhaled antigens. Established airway tolerance might not be sustained in the presence of an innate immunologic stimulus, such as IL-33.