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A7242 - IRF-7 Modulates RIG-I and Antiviral Responses Through Direct Regulation of Interferon Induction During Influenza Infection in Human Airway Epithelia
Author Block: W. Wu, W. Zhang, L. Tian, J. P. Metcalf; University of Oklahoma Health Science Center, Oklahoma City, OK, United States.

RATIONALE: Influenza A (IAV) infection is a major cause of morbidity and mortality. In 2009, a pandemic caused by the novel H1N1 IAV infected over 300,000 individuals with at least 16,000 confirmed deaths worldwide. To combat a viral infection, the host’s immune system must recognize the invader’s foreign material, and develop an effective antiviral response. Retinoic acid-inducible protein I (RIG-I) plays an important role in the recognition of IAV in most cell types, and leads to induction of interferon (IFN), a critical component of the response to influenza infection. In turn, type I IFN induction by RIG-I depends on the transcription factor interferon regulatory factor (IRF-7). There is also positive feedback by IFN on RIG-I mediated IFN induction, though this process is poorly understood. METHODS: We investigated RIG-I and IFN induction by IAV in Bci-NS1, an immortalized human airway basal cell line. Bci-NS1 cells were infected with A/Puerto Rico/8/1934 (PR8) H1N1 IAV at an MOI =1. Virus diluents (mock) were used as negative controls. After 24 h of infection, cells and supernatants were collected for qRT-PCR and western blot to determine RIG-I and IFN mRNA and protein expression levels. Next, we used siRNA against IRF-7 to specifically block IRF-7 expression in these cells in order to determine the role of IRF-7 in the induction of IFN. RESULTS: As expected, we found that the basal expression level of RIG-I was very low in BCi-NS1 cells, and that IAV infection induced robust RIG-I and IFN expression. siRNA against IRF-7 inhibited RIG-I mRNA expression and IFN induction by IAV infection. Most importantly, even without virus infection, IFN-beta alone induced RIG-I, and siRNA against IRF-7 failed to inhibit RIG-I mRNA induction by IFN-beta. CONCLUSIONS: Our results suggest that RIG-I expression is highly inducible and greatly amplified by the first phase of IFN production, and that IRF-7 controls RIG-I expression by directly regulating the first phase of IFN induction during influenza infection in human lung airway epithelial cells. IRF-7 is not, however, involved in the portion of the IFN feedback loop whereby IFN stimulates RIG-I. This discovery will be important in designing strategies for the development of novel treatments for influenza infections.