Naringenin Improves Innate Immune Suppression after PRRSV Infection by Reactivating the RIG-I-MAVS Signaling Pathway, Promoting the Production of IFN-I.

Porcine reproductive and respiratory syndrome (PRRS) has been prevalent for nearly forty years since it was first reported. It has been one of the major diseases jeopardizing the healthy development of the world swine industry, as well as causing great economic losses to the industry's economic development. Furthermore, no way has been found to combat the disease due to the immunosuppressive properties of its pathogen porcine reproductive and respiratory syndrome virus (PRRSV) infection. We previously examined the mRNA expression of IFN-I in PRRSV-infected Marc-145 cells at different time periods using qRT-PCR, and found that the mRNA expression of IFN-I in the late stage of PRRSV infection showed suppression. Naringenin is a flavonoid found in citrus fruits and has a very wide range of pharmacological activities. Therefore, the aim of the present study was to investigate the modulatory effect of naringenin on the suppressed innate immune response after PRRSV infection. The expression of IFN-I, IL-10, and ISGs in the late stage of PRRSV infection was examined using qRT-PCR, and the results showed that naringenin improved the expression of antiviral cytokines suppressed by PRRSV infection. Further results showed that naringenin treatment significantly up-regulated the expression of proteins related to the RIG-I-MAV immune signaling pathway, and that naringenin could not significantly activate the RIG-I-MAVS signaling pathway after the addition of the RIG-I inhibitor Cyclo. Overall, these data demonstrated that naringenin could improve the innate immune response suppressed by PRRSV infection by modulating the RIG-I-MAVS signaling pathway. Therefore, our study will provide a theoretical basis for the development of naringenin as a drug against immunosuppressive viral infectious disease infections.