Effects Of Antibiotics,Lactobacillus And Tryptophan On The Tissue Structure,Intestinal Flora And Microbial Metabolism Of Influenza Virus Infected Mice

The annual pandemic caused by influenza virus poses a great threat to human and animal health.At present,the most effective way to fight influenza virus infection is still to play the immunoprotecive effect of antibody through vaccines.As influenza virus is prone to gene rearrangement in the process of proliferation,different virus subtypes are produced,which greatly reduces the effectiveness of the vaccine.Antibiotics,as a supportive treatment,are also widely used in the treatment of influenza virus complications,but improper use of antibiotics often leads to unsatisfactory treatment results.It is necessary to find other effective ways to relieve the symptoms of the flu virus.An increasing number of studies have focused on the interaction between the lungs and intestines during influenza infection.Our study takes the "lung-intestinal axis" as a foothold to explore the changes in the respiratory and digestive tract,especially the changes in the microbes and metabolites in the intestine after influenza virus infection and antibiotic treatment.In order to explore the regulatory effect of intestinal microorganisms and metabolites on influenza virus infection,lactobacillus and tryptophan were selected as exogenous supplements.The screening of key microorganisms and metabolites provides a new idea for the treatment of intestinal injury,and provides a theoretical basis for the follow-up search for antibiotic substitutes to control and alleviate the lung and intestinal injury caused by influenza.1.Effects of influenza viruse and antibiotics on intestinal microorganismsThe lung and intestine were damaged after influenza virus infection,but the virus was only detected in the lung,and the antibiotic treatment caused more serious tissue damage.The expression of toll-like receptor(TLR)signaling pathway in the lung was significantly increased(P<0.05),and the expression of the downstream cytokine interferon β(IFNβ)of TLR was also significantly increased(P<0.05).The significant expression of IFN-I in the lung induces the changes of intestinal microorganisms,and antibiotic treatment leads to more drastic changes.The diversity of microorganisms decreased significantly(P<0.01).Firmicutes decreased significantly(P<0.001),while Bacteroidetes(P<0.01)and Proteobacteria(P<0.001)increased significantly.Both the influenza infection and antibiotic treatment resulted in a significant increase in enterobacteriaceae(P<0.05)and a significant decrease in lactobacillus(P<0.05).2.Effects of influenza virus and antibiotics on intestinal microbial metabolismBoth the influenza virus infection and antibiotic treatment led to changes in intestinal metabolites.Principal component analysis(PCA)and partial least square discriminant analysis(PLSDA)showed that antibiotics led to more drastic changes in metabolites,which were mainly caused by amino acid metabolism and synthesis.The correlation analysis between metabolites related to typtophan metabolic pathway and intestinal microorganisms showed that the tryptophan metabolic pathway was positive correlation with lactobacillus and negative correlation with enterobacteriaceae.Indoleamine 2,3-dioxygen ase(IDO1),the rate limiting enzyme of tryptophan metabolism,was significantly increased in colon(P<0.01)and decreased in small intestine(P<0.01).The abnormal expression of IDO1 induces an imbalance between Th17 and Treg cells in the intestinal tract.The correlation analysis between metabolites related to intestinal barrier function and microorganisms showed that the metabolites related to intestinal barrier were positively correlated with lactobacillus and negatively correlated with enterobacteriaceae.Influenza virus infection and antibiotic treatment led to a significant decrease in the expression of intestinal epithelial tight junction proteins(P<0.01).3.Regulatory effects of tryptophan and Lactobacillus on influenza virus infectionSupplementation of tryptophan and lactobacillus in mice infected with influenza virus showed that the damage of lung and intestine tissue was reduced,the number of enterobacteriaceae in intestine was significantly reduced(P<0.05),and lactobacillus had no significant change.Liquid chromatography-mass spectrometry(LC-MS)showed that the supplement of tryptophan and lactobacillus made the tryptophan metabolic pathway in the intestinal tract basically return to normal.The addition of tiyptophan had no obvious effect on the activity of IDO1,and the addition of lactobacillus restored the activity of IDO1 to normal basically.The addition of tryptophan and lactobacillus increased the expression of tight junction protein(P<0.05)and improved the epithelial barrier function.In summary,influenza virus infection leads to the damage of lung and intestinal tissue,changes in intestinal microbes and metabolites,imbalance of intestinal T cells,decreased expression of tight junction proteins,and the antibiotics exacerbate these changes.By adding tryptophan and lactobacillus to the gastrointestinal tract,the damage of lung and intestinal tissues was improved.Intestinal microorganisms and metabolites were basically restored to normal,and the expression of tight junction proteins was basically restored to normal.