Repeated exposures to environmental allergens in susceptible individuals drive the development of type 2 inflammatory conditions such as asthma, which have been traditionally considered to be mainly mediated by Th2 cells. However, emerging evidence suggest that a new innate cell type, group 2 innate lymphoid cells (ILC2), plays a central role in initiating and amplifying a type 2 response, even in the absence of adaptive immunity. At present, the regulatory mechanisms for controlling ILC2 activation remain poorly understood. Here we report that respiratory delivery of immunogenic extracellular RNA (exRNAs) derived from RNA- and DNA-virus infected cells, was able to activate a protective response against acute type 2 lung immunopathology and airway hyperresponsiveness (AHR) induced by IL-33 and a fungal allergen, A. flavus, in mice. Mechanistically, we found that the innate immune responses triggered by exRNAs had a potent suppressive effect in vivo on the proliferation and function of ILC2 without the involvement of adaptive immunity. We further provided the loss-of-function genetic evidence that the TLR3- and MAVS-mediated signaling axis is essential for the inhibitory effects of exRNAs in mouse lungs. Thus, our results indicate that the host detection of extracellular immunostimulatory RNAs generated during respiratory viral infections have an important function in the regulation of ILC2-driven acute lung inflammation.
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