A20 is a master switch of IL-33 signaling in macrophages and determines IL-33–induced lung immunity

Background IL-33 plays a major role in the pathogenesis of allergic diseases such as asthma and atopic dermatitis. On its release from lung epithelial cells, IL-33 primarily drives type 2 immune responses, accompanied by eosinophilia and robust production of IL-4, IL-5, and IL-13. However, several studies show that IL-33 can also drive a type 1 immune response. Objective We sought to determine the role of A20 in the regulation of IL-33 signaling in macrophages and IL-33–induced lung immunity. Methods We studied the immunologic response in lungs of IL-33–treated mice that specifically lack A20 in myeloid cells. We also analyzed IL-33 signaling in A20-deficient bone marrow–derived macrophages. Results IL-33–induced lung innate lymphoid cell type 2 expansion, type 2 cytokine production, and eosinophilia were drastically reduced in the absence of macrophage A20 expression, whereas neutrophils and interstitial macrophages in lungs were increased. In vitro, IL-33–mediated nuclear factor kappa B activation was only weakly affected in A20-deficient macrophages. However, in the absence of A20, IL-33 gained the ability to activate signal transducer and activator of transcription 1 (STAT1) signaling and STAT1-dependent gene expression. Surprisingly, A20-deficient macrophages produced IFN-γ in response to IL-33, which was fully STAT1-dependent. Furthermore, STAT1 deficiency partially restored the ability of IL-33 to induce ILC2 expansion and eosinophilia in myeloid cell–specific A20 knockout mice. Conclusions We reveal a novel role for A20 as a negative regulator of IL-33–induced STAT1 signaling and IFN-γ production in macrophages, which determines lung immune responses. IL-33 plays a major role in the pathogenesis of allergic diseases such as asthma and atopic dermatitis. On its release from lung epithelial cells, IL-33 primarily drives type 2 immune responses, accompanied by eosinophilia and robust production of IL-4, IL-5, and IL-13. However, several studies show that IL-33 can also drive a type 1 immune response. We sought to determine the role of A20 in the regulation of IL-33 signaling in macrophages and IL-33–induced lung immunity. We studied the immunologic response in lungs of IL-33–treated mice that specifically lack A20 in myeloid cells. We also analyzed IL-33 signaling in A20-deficient bone marrow–derived macrophages. IL-33–induced lung innate lymphoid cell type 2 expansion, type 2 cytokine production, and eosinophilia were drastically reduced in the absence of macrophage A20 expression, whereas neutrophils and interstitial macrophages in lungs were increased. In vitro, IL-33–mediated nuclear factor kappa B activation was only weakly affected in A20-deficient macrophages. However, in the absence of A20, IL-33 gained the ability to activate signal transducer and activator of transcription 1 (STAT1) signaling and STAT1-dependent gene expression. Surprisingly, A20-deficient macrophages produced IFN-γ in response to IL-33, which was fully STAT1-dependent. Furthermore, STAT1 deficiency partially restored the ability of IL-33 to induce ILC2 expansion and eosinophilia in myeloid cell–specific A20 knockout mice. We reveal a novel role for A20 as a negative regulator of IL-33–induced STAT1 signaling and IFN-γ production in macrophages, which determines lung immune responses.