Hitomi Tanaka,1 Shigeki Katoh,1 Kazuko Uno,2 Toru Oga1

1 Department of Respiratory Medicine, Kawasaki Medical School, Okayama, Japan
2 Louis Pasteur Center for Medical Research, Kyoto, Japan

Abstract

Background: Interleukin (IL)-5 is essential for allergen induced eosinophilic airway inflammation, but not activation of T helper type 2 (Th2) cells in the lung. Although an excessive Th2 reaction is observed without IL-5 signaling, the mechanisms have remained unknown.
Objective: To evaluate the negative-feedback mechanism in eosinophilic airway inflammation, we examined IL-33 triggered eosinophilic airway inflammation in IL-5Rα-/- mice.
Methods: Mice were administered intranasal IL-33 for 3 days. Airway hyperresponsiveness (AHR) was evaluated and bronchoalveolar lavage (BAL) was performed 24 h after the last IL-33 treatment. The number of inflammatory cells and cytokine levels in the BAL fluid (BALF) were analyzed, and histologic examination was performed.
Results: Compared with IL-33 treated wild-type (WT) mice, intranasal administration of IL-33 in IL-5Rα-/- mice reduced eosinophilic airway inflammation, AHR, and basement membrane thickening, while we found excessive IL-33 induced IL-5 and IL-13 production in the airway without IL-5 signaling. The numbers of eosinophils with a ring-shaped nucleus (resident) and segmented nucleus (inflammatory) were increased in WT mice, but not in IL-5Rα-/- mice following intranasal administration of IL-33, and the numbers of SiglecF-positive eosinophils with (resident) or without (inflammatory) expression of CD62L were also significantly increased by IL-33 treatment in WT mice, but not in IL-5Rα-/- mice. The number of ILC2 cells in the BALF was significantly higher in IL-33 treated IL-5Rα-/- mice than in IL-33 treated WT mice.
Conclusion: These findings suggest the possibility that IL-5 induced eosinophils contribute to the negative-feedback mechanisms in IL-33 induced ILC2 mediated airway inflammation.
Key words: IL-5Rα-/- mice, IL-33, airway inflammation, eosinophil, ILC2