Study On The Imbalance Of Th17/Treg Cell Proportion In Lung Of Balb/c Suckling Mice Infected With Respiratory Syncytial Virus Mediating Intestinal Immune Damage And Gut Microbiota Disorder

Objective: Respiratory syncytial virus(RSV)is the most common pathogen that causes acute respiratory infection in infants and young children,and the immune response caused by RSV is also closely related to the changes in the composition and function of gastrointestinal microorganisms.In order to analyze the pathogenic mechanism of RSV infection and its effect on intestinal flora,we established a model of lung infection in suckling mice,which is similar to infant immune level and susceptible to virus infection,to detect the changes of Th17,Treg cells,related inflammatory factors and intestinal flora.This study can provide new insights for the pathogenesis of RSV infection and the relationship between pulmonary and intestinal axis,and provide new understanding for the treatment of children with RSV infection.Method: 7-day-old Balb/c suckling mice with RSV nose infection were used to establish a lung infection model.Normal control group,PBS control group and virus infection group were established.Lung,small intestine,colon and rectum of each group were collected.(1)HE staining was used to observe the pathological changes of the lungs;(2)Real-time PCR was used to detect the expression of RSV-F protein,ROR-γt and Foxp3 m RNA in lung,small intestine and colon tissue of each group(3)Changes in the contents of IFN-γ,IL-17,IL-22,IL-10 and RegⅢγ in the supernatants of lung,small intestine and colontissues were detected by enzyme-linked immunosorbent assay(ELISA);(4)High-throughput sequencing to detect changes in bacterial flora in rectal tissues.Result:(1)Compared with the normal group,HE staining showed that with RSV infection,as the infection time prolonged,the alveolar structure was gradually aggravated,and the degree of inflammatory cell infiltration gradually increased,which was most significant on the third day after infection.Then the infection gradually improved.(2)Real-time PCR results showed that the ROR-γt and Foxp3 m RNAs in the PBS group were not significantly different from those in the normal group.Compared with the normal group,RSV-F protein m RNA level in the lung tissue was highest on the third day after RSV infection,ROR-γt was highest on the third day,Foxp3 was highest on the fourth day.RSV-F protein m RNA wasn’t detected in the colon and small intestine,ROR-γt was highest on the second day after infection,and Foxp3 was on the third day after infection.(3)The ELISA results showed that compared with the normal group,the IFN-γ content was highest on the third day after infection,and then began to decrease.The changes of IL-17,IL-22,IL-10 and RegⅢγ all increased firstly and then decreased.IL-17 and IL-22 in lung tissue reached the maximum on the third day after infection.IL-10 reached the maximum on fourth days;IL-17 and IL-22 in the small intestine and colon were the largest on the second day after infection,IL-10 was the largest on the third day after infection,and RegⅢγ was the largest on the third day after infection.The difference was statistically significance.(4)The high-throughput sequencing results showed that compared with the normal group,the intestinal flora richness and diversity of the RSV infected group did not change significantly,but the composition of the flora changed significantly.Conclusions: RSV infection of 7-day-old Balb/c suckling mice caused lung inflammation and Th17/Treg imbalance.IL-22-induced overexpression of RegⅢγ led to Th17/Treg development disorder and changes of bacterial composition in the intestine,resulting in intestinal immune damage and bacterial disorder.