The Role Of Host Factor LCN2 And IRG1 In The Inflammatory Response Induced By Influenza A Virus Infection

BackgroundInfluenza is one of the most significant respiratory diseases worldwide result from influenza virus infection.Due to the high mutation frequency of influenza A virus antigen,it has caused large epidemics and presented a serious health threat to human.Currently,the drugs used to treat influenza target the influenza virus,and there are always concerns about drug resistant mutations in the treatment of influenza.It is an urgent need to explore new treatment strategies.Host factors are involved in influenza virus replication and play an important role in the immune response induced by influenza.The aim of this research was to explore the changes of host factors and immune function during influenza A virus infection,and find important host factors and explore related functions during influenza A virus infection.Methods(1)Bioinformatics analysis methods including gene differential expression analysis,GO enrichment analysis,KEGG pathway analysis and GSVA were used to comprehensively analyze the sequencing data of mice and patients with influenza A virus infection in GEO database,to explore the changes of host factors and immune function during influenza A virus infection,and to find the important host factors.(2)ELISA was used to quantify the expression of key host factors in plasma of influenza A patients hospitalized in Pulmonary and Critical Care Medicine of China-Japan Friendship Hospital during 2018-2019 and 2019-2020 influenza seasons,and to explore the relationship between host factors and disease development and prognosis.Moreover,the possible role of host factors in influenza was explored by combining the sequencing data of influenza A patients in GEO database.(3)The animal and cell models of influenza A virus infection were established,and the expression levels of host factors were detected by ELISA,PCR and Western blot.The host factor knock-down cell lines were constructed by lentivirus interference,and the effects of host factors on viral replication and inflammatory cytokines(IL-1β,IL-6 and TNF-α)during influenza A virus infection in vitro were investigated by ELISA,PCR and Western blot.Results(1)Influenza A virus infection induced a wide variety of host factors and significantly up-regulation of interferon response and inflammatory response.Influenza A virus infection significantly increased the proportion of mononuclear macrophages and neutrophil in the lung and mononuclear macrophages and neutrophils mediated major inflammatory response.Neutrophil function was involved in the severe development of influenza A patients.Finally,two important host factors LCN2 and IRG1 were screened out during influenza A virus infection.(2)Host factor LCN2 was increased in peripheral blood of patients infected with influenza A virus,and its expression level was positively correlated with severe disease and poor prognosis of patients.Moreover,LCN2 might be related to neutrophil function in severe patients.(3)In mouse model of influenza A virus infection,virus induced up-regulation of LCN2 and IRG1 in mouse lung tissue.In cell model of influenza A virus infection,expression level of LCN2 was increased in A549 cells infected by influenza A virus.LCN2 did not affect virus replication in A549 cells,and promoted the expression of inflammatory cytokines(IL-1β,IL-6 and TNF-α)in neutrophils.The expression level of IRG1 was increased in macrophages infected by influenza A virus,and IRG1 inhibited the expression of inflammatory cytokine s(IL-1β,IL-6 and TNF-α)in macrophages.Conclusions(1)Influenza A virus infection induces up-regulation of host interferon response and inflammatory response.Neutrophils and mononuclear macrophages mediate the main inflammatory response,and neutrophils play an important role in the development of severe influenza.(2)Influenza A virus infection induces a wide variety of host factors,including upregulation of host factors LCN2 and IRG1.(3)Plasma protein level of LCN2 is increased in patients with influenza A virus infection,and is positively correlated with severe disease and poor prognosis of patients,which maight be used as a potential biomarker for predicting the severity and prognosis of patients.(4)Host factor LCN2 promotes the expression of inflammatory factors in neutrophil,and host factor IRG1 inhibits the expression of inflammatory factors in macrophage.LCN2 and IRG1 have potential regulatory effect in inflammatory response induced by influenza A virus infection,providing an idea for the treatment of immune inflammatory response targeting host factors.