Gallic acid attenuates allergic airway inflammation via suppressed interleukin-33 and group 2 innate lymphoid cells in ovalbumin-induced asthma in mice.

BACKGROUND: Asthma is an inflammatory disease characterized by airway hyperresponsiveness. Gallic acid is a powerful anti-inflammatory agent. In this study we aimed to investigate the efficacy of gallic acid in asthma treatment and its mechanisms.
METHODS: An ovalbumin-induced asthma mouse model was generated. Pro-inflammatory cell infiltration and T helper (Th2)-associated cytokine release in the bronchoalveolar lavage fluid (BALF) were analyzed to reflect the severity of asthma in mice. An interleukin-33 (IL-33)-induced asthma mouse model was also generated to study the mechanism by which gallic acid could improve asthma. Group 2 lymphoid cells (ILC2s) were identified using flow cytometry. Proteins were detected using Western blotting.
RESULTS: Ovalbumin significantly increased the infiltration of pro-inflammatory cells, including eosinophils, macrophages, lymphocytes, and neutrophils, accompanied by enhanced airway hyperesponsiveness. Gallic acid reduced pro-inflammatory cell infiltration and improved airway hyperresponsiveness. Meanwhile, gallic acid reduced IL-5 and IL-13 levels in BALF and decreased expression of IL-33 in the lungs. Mechanistically, gallic acid inhibited MyD88 expression and downregulated nuclear factor (NF)-κB signaling to decrease IL-33 expression.
CONCLUSIONS: Gallic acid can mollify ovalbumin-induced asthma in mice, possibly by inhibiting IL-33-mediated ILC2 activation and subsequent Th2 cytokine release via downregulation of the MyD88/NF-κB signaling pathway. ©2018 ARSAAOA, LLC.