Interleukin‐33 Deficiency Protects the Skin From Ulcer Formation in an Ischemia–Reperfusion‐Induced Decubitus Mouse Model

Interleukin-33 (IL-33) is an alarmin released upon epithelial tissue damage. It functions as a nuclear factor for regulating gene expression. We hypothesised that IL-33 is involved in the formation of decubitus ulcers through damaged epidermis. Therefore, this study aimed to clarify the mechanism of IL-33 action in decubitus ulcer formation. IL-33 knockout (KO), soluble stimulation-2 (ST2) transgenic, and wild-type (WT) mice were used to construct an ischemia-reperfusion (I/R) injury as a decubitus model. The ulcer area was significantly reduced in IL-33 KO mice compared to WT mice but was not reduced in ST2 transgenic mice. Anti-IL-33 receptor (transmembrane ST2) antibodies effectively prevented ulcer formation; however, an anti-IL-33 neutralising antibody was ineffective. The number of infiltrating macrophages was higher, while that of neutrophils and mast cells was lower in IL-33 KO mice than in WT mice. The number of M2 macrophages increased in IL-33 KO mice. Characterisation of gene expression levels revealed significantly reduced interleukin-1 beta (IL-1β) and increased C-C motif chemokine ligand 17 expression in IL-33 KO mice. Macrophages isolated from ulcers in WT or IL-33 KO mice stimulated with exogenous IL-33 produced comparable amounts of IL-1β. In conclusion, our study indicates that IL-33 is released in response to I/R injury in the skin, contributing to inflammatory macrophage and mast cell infiltration and stimulation, resulting in IL-1β production and the massive infiltration of effector cells, including neutrophils, which finally induces decubitus ulcer formation. These results suggest that suppressing IL-33 expression could be beneficial for treating early-phase decubitus ulcers.