The Effects And Mechanism Of Lipolysaccharide On Airway Inflammtion And Airway Hyperreactibity Induced By Respiratory Syncytial Virus Infected Mice

Background: Respiratory syncytial virus (RSV) is the main pathogenof lower respiratory infection in infants and young children under five yearsold. RSV infection, especially severe RSV infection, in infants and youngchildren is closely related to children’s persistent wheezing and airwayhyperreactivity (AHR). Severe RSV infection often merges bacterialinfection, and gives priority to with gram-negative bacteria infection.Lipopolysaccharide（LPS） is a major component of gram-negativebacteria. Our preliminary study showed: the concentration of IL-6wasincreased in the RSV infected epithelial cells after LPS stimulation.However, the LPS effect on RSV infection is not clear in vivo. This studysuccessfully established RSV infection animal model with LPS stimulationin mice, then observed the airway inflammation and AHR of this model anddiscussed the possible mechanism.Methods: Female,6-8weeks old BALB/c mice were divided into4groups: Control group, LPS group, RSV group and RSV+LPS group. Five,seven and fourteen days after RSV innoculation, viral copy number wasdetected by Q-PCR; infiltration of inflammatory cells in BALF, lung tissuedamage as well as AHR were assessed; expression of TRIF and MyD88inthe lung tissue were measured by Western blotting, concentration of IFN-γ,KC, MMP-9and IL-6in BALF were detected by ELISA.Results: Viral copy number: Viral copy number of RSV+LPS group was not bigger than that of RSV group. Total cells and subset cells: Totalcells of LPS, RSV and RSV+LPS group were remarkably higher than that ofControl group at5,7and14days post RSV infection. LPS group was givenpriority to with neutrophil, while RSV group was lymphocyte andRSV+LPS group was neutrophil. Histopathological changes: Lung tissuedamage were significantly increased in LPS and RSV group5and7dayspost RSV infection. While lung tissue damage were significantly increasedin RSV+LPS group5,7and14days post RSV infection. AHR: AHR wasmeasured in LPS group only5days post RSV infection. While AHR wasmeasured in RSV and RSV+LPS group5,7and14days post RSVinfection. AHR in RSV+LPS group was higher than that of RSV group5,7and14days post RSV infection, especially14days post RSV infection.Expression of TRIF and MyD88: Seven days after RSV infection,expression level of TRIF was dramatically higher in the RSV+LPS groupcompared with that of Control group, while LPS and RSV group was a littlehigher than that of Control group. Expression levels of MyD88showed nodifference among the4groups. Cytokine: The main cytokines in BALF ofLPS group were KC and MMP-9, while RSV group was IFN-γ andRSV+LPS group were IFN-γ, KC and MMP-9. High level of KC andMMP-9in BALF were lasted longer in RSV+LPS group.Conclusion: LPS could aggravate airway inflammation and AHR byactivating TRIF-KC/MMP-9signal pathway to recruit neutrophil in RSVinfected mice.