Research On The Developmental Characteristics Of Mouse Lung Microbiome And The Mechanism Of Early Flora Homeostasis Regulating Antiviral Immune Function

The human microbiome is closely related to the regulation of immune homeostasis,which is associated with the development of various diseases.Studies have found that early colonization of intestinal microbes in infants and young children promotes the development of the immune system and the formation of immune memory.Early microbial dysregulation is closely related to the increased risk of inflammatory bowel disease,allergies and asthma in adulthood.Existing studies suggest that there is a critical window period for the development of the microbiome and interaction with the immune system.Interference with this period will lead to irreversible defects in the development and function of immune cells.Therefore,research on the developmental characteristics of microbiota is helpful.Elucidating the critical period of establishment of the microbiota homeostasis,and thus helping to reveal the functional microbiome associated with immune regulation and related diseases provide new effective intervention targets.The respiratory tract is an organ that communicates with the outside world.There are also commensal microbial groups in the respiratory tract.The steady state of the airway microbiota is closely related to the immune defense function of the respiratory system.It has been suggested that as a mucosal covering system in the body,the intestinal microbiome may regulate functional homeostasis of the lung microbiome,and the presence of the“gut-lung axis”provides a new perspective for intervention strategies for the discovery of respiratory diseases from a microbiological perspective.However,the current research on the respiratory microbiome is still very limited.Whether it is regulated by the intestinal microbiome during physiological development,its role and mechanism in anti-viral infection immune defense is not fully understood.Therefore,this study intends to analyze the microbial characteristics of the mouse lung development,reveal the axis mechanism of its developmental process,interfere with the microbial group homeostasis through early antibiotic intervention,and discover the microbial group and its mechanism of action related to antiviral immune function.The 16S rRNA sequencing method was used to analyze the microbial composition and dynamic changes of the lungs in the day after birth(Day 1,D01),D03,D05,D07,D14,D21,D28 and D56.The microbiome group reached a relatively stable state,which was significantly different from the development of the intestinal microbial group.The intestinal microbiome group showed a significant increase in the amount of bacteria and a diversity from 1 week to 3 weeks after birth(P<0.01).D01 and D07-D21 are important periods of development of the commensal microbial group in the lung and intestine,respectively.The correlation analysis of lung and gut microbiome development time series showed that the lungs in the early development(D01-D14)were significantly associated with the increase of OTU abundance in the gut-specific bacteria,including Haemophilus(r=0.38,p<0.001)and so on.By directing antibiotic intervention,the abundance of specific bacteria associated with lung development in the lung is reduced.Further,a metabolome analysis was performed on the antibiotic intervention group and the control group,and it was found that metabolites such as proline in the intestine were significantly associated with OTU such as Haemophilus in the lung(p<0.05),suggesting that the intestinal microbes were responsible for lung microbes.The effect may be achieved through regulation of intestinal metabolites.The intestinal permeability of mice at 1 week,2 weeks and 3 weeks old showed that the intestinal permeability in the early stage of development(1-2 weeks)was significantly higher than that in 3 weeks old mice(p<0.05),further suggesting that the effects of intestinal microbes on lung microbes may also be achieved through changes in intestinal permeability.To further reveal the effects of antibiotic exposure on mouse microbial homeostasis and the effects and mechanisms of antiviral immunity,we established an early microbial group steady-state intervention model.The lung and intestinal microbiota composition of D07,D14,D21,D28 and D 56 mice after birth was characterized by the administration of antibiotics to pregnant mice and 7 days after birth,which interfered with the colonization of the intestines and lungs of mouse.The results showed that the microbial composition of D56 in the early antibiotic-exposed mice was significantly different from that in the control group(p<0.01),which compared with the existing studies and found that the antibiotic exposure colonization of the adult population was less disturbed.The results of faster recovery are different,suggesting that the colonization of early symbiotic bacteria is crucial for the establishment of mouse microbial group homeostasis.In mice exposed to early antibiotics,the influenza virus was used to attack the lungs in adulthood.Compared with the control group,the body weight and survival rates of the antibiotic exposure group were significantly lower(p<0.05),and the lung inflammation level and pathological damage were heavier;Co-housing to restore the intestinal flora of the antibiotic-exposed group still affects the anti-viral immunity of adult mouse.The proportion of bone marrow hematopoietic stem cells and pluripotent progenitor cells in the early exposure group of antibiotics was significantly increased(p<0.05),the proportion of myeloid progenitor cells was significantly decreased(p<0.01),the function of bone marrow immune cells was inhibited,and peripheral immune cell function was observed.Excessive activation may be one of the mechanisms of excessive inflammatory damage after viral infection.In addition,the intestinal metabolome analysis showed that the intestinal proline metabolism pathway was significantly activated in adult early exposure to antibiotics(p=0.0011),whether the activation of specific amino acids is related to immune cell dysfunction needs further research.This study systematically analyzed the composition and dynamics of the microbial composition of the lungs during mouse development,which was associated with the development of specific bacteria of the gut microbiome and reveals that small molecule metabolites such as proline may be factors in the development of pulmonary microbiome,enriching the theory of the regulation axis of the gut microbiota.An antibiotic intervention model of the pulmonary microbial group was established to explain the effect of the microbial group on the anti-viral immune function in the early development stage,and further provided a new idea for regulating the antiviral immunity of the lung through intestinal microbial intervention.