Roles Of Pattern Recognition Receptor Melanoma Differentiation Associated Gene 5 And Heat Shock In Inluenza A Virus Infection

There are different pattern recognition receptors (PRRs) in the cell could detect the pathogen-associated molecular patterns (PAMPs). The detection of PAMPs could induce the expression of pro-inflammatory cytokines and activate the antiviral response. Influenza A virus (IAV) could be recognized by toll-like receptors (TLRs), NOD-like receptors (NLRs) and RIG-I-like receptors (RLRs). The RLRs family contains RIG-I, MDA5 and LGP2. It is known that the detection of IAV is based on RIG-I, which could induce the interferon expression and start the antiviral response. However, in recently study, researchers found MDA5, a PRR that is generally believed to recognize complex dsRNA, a PAMP not associated with IAV infection, plays an important role in influenza infection. In present study, we generated MDA5 gene knockout cell line and used the MDA5 deficiency mice in order to further understanding innate immune response against influenza virus infection.We used CRISPR/Cas9 system and generated an MDA5 (IFIH1) gene knockout A549 cell line. We found MDA5 was associated with influenza infection, increased the virus replication and induced the downstream interferon response in vitro. In addition, we found MDA5 deficiency (KO) mice had less lung injury, lower mortality and less weight loss compared with the wide type (WT) mice. Data showed that the viral titer in KO mice was lower than WT mice. At 3d.p.i the neutrophils were not rised in KO mice. The qPCR data showed the mRNA level of the cytokines in KO mice were lower than the WT mice at 3d.p.i. These data showed that MDA5 is associated with the IAV infection and could increase the viral replication and induce the IFNs response. Interestingly, we found high expression of interferons in KO mice at 6d.p.i. The defective viral genomes (DVGs) were detected in the lung tissues after infection and accumulated more in KO mice. In this study, we investigated the role of MDA5 in influenza virus infection. We also find that the generation of influenza DVGs is interacted with MDA5.The over expression of the cytokines is associated with’ cytokine storm’ that leads to acute lung inflammation. In this study, mice were treated at 39℃ for 4 h before infected, with H5N1 HPAIV. The surivial rate of the heat-shocked mice was 57% while the WT mice had died by 11d.p.i. Following the HPAIV H5N1 infection, short-term heat shock alleviated immunopathology and viral replication in lung tissue, and repressed the weight loss and increased the survival rate of H5N i-infected mice. Interestingly, short-term heat shock significantly increased the levels of HSP70 and reduced pro-inflammatory cytokines expression of IL-6, TNF-α, IFN-β and IFN-y in the lung tissues of infected mice. Our data reported that short-term heat shock presented beneficial anti-HPAIV H5N1 properties in mice model.