The study investigates the distinct roles of RIG-I and MDA5 in the innate immune response to RNA viruses. RIG-I and MDA5 are cytoplasmic helicases that detect viral RNA and trigger interferon production through the adaptor protein IPS-1. The research compares the signaling requirements of RIG-I, MDA5, and IPS-1 in response to various RNA viruses, including paramyxoviruses, orthomyxoviruses, and reoviruses. Key findings include: 1. **Paramyxoviruses**: RIG-I is essential for triggering the innate immune response to paramyxoviruses, such as Sendai virus (SenV) and Newcastle disease virus (NDV). In contrast, MDA5 is not essential but may play an auxiliary role in amplifying the response. 2. **Dengue virus (DEN) and reoviruses**: DEN2 and reoviruses can trigger the innate immune response independently of RIG-I or MDA5. However, IPS-1 is essential for signaling the innate immune response to these viruses. 3. **Orthomyxoviruses**: RIG-I is essential for the innate immune response to influenza A and B viruses. The viruses signal through IPS-1, which is required for IRF-3 activation and ISG expression. 4. **Functional Genomics Analyses**: Influenza A virus infection triggers the expression of immune system-related genes in the absence of RIG-I, indicating that RIG-I plays a crucial role in regulating these genes. The study concludes that IPS-1 is essential for the innate immune response to RNA viruses, while RIG-I and MDA5 have distinct and redundant roles in pathogen recognition and signaling. These findings provide insights into the mechanisms of RNA virus infection and potential targets for antiviral strategies.The study investigates the distinct roles of RIG-I and MDA5 in the innate immune response to RNA viruses. RIG-I and MDA5 are cytoplasmic helicases that detect viral RNA and trigger interferon production through the adaptor protein IPS-1. The research compares the signaling requirements of RIG-I, MDA5, and IPS-1 in response to various RNA viruses, including paramyxoviruses, orthomyxoviruses, and reoviruses. Key findings include: 1. **Paramyxoviruses**: RIG-I is essential for triggering the innate immune response to paramyxoviruses, such as Sendai virus (SenV) and Newcastle disease virus (NDV). In contrast, MDA5 is not essential but may play an auxiliary role in amplifying the response. 2. **Dengue virus (DEN) and reoviruses**: DEN2 and reoviruses can trigger the innate immune response independently of RIG-I or MDA5. However, IPS-1 is essential for signaling the innate immune response to these viruses. 3. **Orthomyxoviruses**: RIG-I is essential for the innate immune response to influenza A and B viruses. The viruses signal through IPS-1, which is required for IRF-3 activation and ISG expression. 4. **Functional Genomics Analyses**: Influenza A virus infection triggers the expression of immune system-related genes in the absence of RIG-I, indicating that RIG-I plays a crucial role in regulating these genes. The study concludes that IPS-1 is essential for the innate immune response to RNA viruses, while RIG-I and MDA5 have distinct and redundant roles in pathogen recognition and signaling. These findings provide insights into the mechanisms of RNA virus infection and potential targets for antiviral strategies.