Porcine reproductive and respiratory syndrome (PRRS) is an epidemic animal infectious disease worldwide, causing huge economic losses to the global swine industry. Fas-associated death domain (FADD) was previously reported to be an adaptor protein that functions in transferring the apoptotic signals regulated by the death receptors. In the current study, we unravel its unidentified role in promoting type I interferon (IFN) production during PRRS virus (PRRSV) infection. We identified that FADD inhibited PRRSV infection via promotion of type I IFN transcription. Overexpression of FADD suppressed the replication of PRRSV, while knockout of FADD increased viral titer and nucleocapsid protein expression. Mechanistically, FADD promoted mitochondrial antiviral signaling protein (MAVS)-mediated production of IFN-β and some IFN-stimulated genes (ISGs). Furthermore, FADD exerted anti-PRRSV effects in a MAVS-dependent manner and increased the type I IFN signaling during PRRSV infection. This study highlights the importance of FADD in PRRSV replication, which may have implications for the future control of PRRS.

Porcine reproductive and respiratory syndrome virus (PRRSV) remains one of the most important pathogens, resulting in huge economic losses to the global pig industry. Ipriflavone is an isoflavone derivative involved in various biological processes, showing anti-inflammatory, anti-apoptotic, antioxidant, and neuroprotective effects. However, the role of ipriflavone in antiviral immune response to PRRSV is unknown. In this study, we discovered that ipriflavone could significantly inhibit PRRSV replication. Moreover, ipriflavone inhibited PRRSV replication regardless of whether ipriflavone was added pre-, co-, or post-PRRSV infection, and ipriflavone mainly inhibited virus replication and assembly stages. Importantly, ipriflavone had the capacity to upregulate the expression levels of IFN-β and ISG56. Additionally, ipriflavone promoted the expression of RIG-I and MAVS, and induced phosphorylation of IRF3 and STAT1, while reducing PRRSV replication. Collectively, ipriflavone could enhance the RIG-I/IRF3 signaling pathway, thereby inhibiting PRRSV replication. These findings will provide an important theoretical basis for the development of therapeutic agents against PRRSV infection.