2′3′-cGAMP is known as a nonclassical second messenger and small immune modulator that possesses potent antitumor and antiviral activities via inducing the stimulator of IFN genes–mediated (STING-mediated) signaling pathway. However, its function in regulating type 2 immune responses remains unknown. Therefore, we sought to determine a role of STING activation by 2′3′-cGAMP in type 2 inflammatory reactions in multiple mouse models of eosinophilic asthma. We discovered that 2′3′-cGAMP administration strongly attenuated type 2 lung immunopathology and airway hyperreactivity induced by IL-33 and a fungal allergen, Aspergillus flavus . Mechanistically, upon the respiratory delivery, 2′3′-cGAMP was mainly internalized by alveolar macrophages, in which it activated the STING/IFN regulatory factor 3/type I IFN signaling axis to induce the production of inhibitory factors containing IFN-α, which blocked the IL-33–mediated activation of group 2 innate lymphoid (ILC2) cells in vivo. We further demonstrated that 2′3′-cGAMP directly suppressed the proliferation and function of both human and mouse ILC2 cells in vitro. Taken together, our findings suggest that STING activation by 2′3′-cGAMP in alveolar macrophages and ILC2 cells can negatively regulate type 2 immune responses, implying that the respiratory delivery of 2′3′-cGAMP might be further developed as an alternative strategy for treating type 2 immunopathologic diseases such as eosinophilic asthma.

The innate immune sensing of allergens or allergen-associated components regulate the development of type 2 inflammatory responses. However, the underlying molecular basis by which allergens or allergen-associated components are detected by innate immune receptors remains elusive. In this study, we report that the most common aeroallergen, house dust mite (HDM), harbors a dsRNA species (HDM-dsRNA) that can activate TLR3-mediated IFN responses and counteract the development of an uncontrolled type 2 immune response. We demonstrate that the mouse strains defective in the dsRNA-sensing pathways show aggravated type 2 inflammation defined by severe eosinophilia, elevated level of type 2 cytokines, and mucus overproduction in a model of allergic lung inflammation. The inability to sense HDM-dsRNA resulted in significant increases in airway hyperreactivity. We further show that the administration of the purified HDM-dsRNA at a low dose is sufficient to induce an immune response to prevent the onset of a severe type 2 lung inflammation. Collectively, these results unveil a new role for the HDM-dsRNA/TLR3–signaling axis in the modulation of a type 2 lung inflammation in mice.