RIG-I overexpression decreases mortality of cigarette smoke exposed mice during influenza A virus infection

Background: Retinoic acid-inducible gene I (RIG-I) is an important regulator of virus-induced antiviral interferons (IFNs) and proinflammatory cytokines which participate in clearing viral infections. Cigarette smoke (CS) exposure increases the frequency and severity of respiratory tract infections. Methods: We generated a RIG-I transgenic (TG) mouse strain that expresses the RIG-I gene product under the control of the human lung specific surfactant protein C promoter. We compared the mortality and host immune responses of RIG-I TG mice and their litter-matched wild type (WT) mice following challenge with influenza A virus (IAV). Results: RIG-I overexpression increased survival of IAV-infected mice. CS exposure increased mortality in WT mice infected with IAV. Remarkably, the effect of RIG-I overexpression on survival during IAV infection was enhanced in CS-exposed animals. CS-exposed IAV-infected WT mice had a suppressed innate response profile in the lung compared to sham-exposed IAV-infected WT mice in terms of the protein concentration, total cell count and inflammatory cell composition in the bronchoalveolar lavage fluid. RIG-I overexpression restored the innate immune response in CS-exposed mice to that seen in sham-exposed WT mice during IAV infection, and is likely responsible for enhanced survival in RIG-I TG mice as restoration preceded death of the animals. Conclusions: Our results demonstrate that RIG-I overexpression in mice is protective for CS enhanced susceptibility of smokers to influenza infection, and that CS mediated RIG-I suppression may be partially responsible for the increased morbidity and mortality of the mice exposed to IAV. Thus, optimizing the RIG-I response may be an important treatment strategy for CS-enhanced lung infections, particularly those due to IAV.