64: Identification of two distinct mechanisms that control the duration of the interferon-mediated antiviral response

The innate antiviral response mainly relies on the production of type I interferons (IFN α / β ) . IFNs establish a robust antiviral state through the induction of hundreds of interferon-stimulated genes (ISGs), which restrict virus replication and spreading. The inability of the host to sustain an antiviral response leads to failure in eradicating the infection. Conversely, uncontrolled duration of the antiviral response is associated with the development of autoimmune disorders. To reach the ideal duration for efficient fighting of the infection without generation of side effects, the antiviral response needs to be strictly regulated. However, these mechanisms are still barely characterized. We are studying the duration of the antiviral response against Paramyxoviruses in human airway epithelial cells. We performed a thorough analysis of the temporal involvement RIG-I and MDA5 in the regulation of IRF-3, a key regulator of the IFNB gene. Based on specific RNAi-mediated knockdown of RIG-I or MDA5, we unveiled that while RIG-I is critical for the initiation of IRF-3 activation, MDA5 rather prevents active IRF-3 degradation, thereby sustaining IRF-3 activation and downstream gene expression. Conversely, ectopic expression of MDA5 prolonged RIG-I-induced IRF-3 activation. Once IFNs are produced, they promote the expression of ISGs. The proinflammatory cytokine TNF α is secreted concomitantly to IFN β and was shown to act synergistically to trigger a delayed specific antiviral transcriptional program. We identified the DUOX2 and DUOXA2 genes amongst the late genes specifically induced by IFN β /TNF α . These genes encode for the H 2 O 2 -producing DUOX2 enzyme and its activator DUOXA2. Using a RNAi approach, we found that DUOX2-mediated extracellular H 2 O 2 release in human airway epithelial cells is required to sustain the level of IFN β and IFN λ at late time of infection. Altogether, our results identified two novel mechanisms that contribute to the duration of the IFN-mediated antiviral response in response to Paramyxoviruses.