Effects Of Short-term Exposure To Atmospheric PM_2.5 On Innate Immune Function Of The Airways:a Panel Study Of College Students

BackgroundAir pollution is a global prominent environmental and public health problem.The respiratory system is the initial contact and main impact site of fine particulate matter(PM_2.5)inhalation.Epidemiological studies have shown a positive correlation between PM_2.5exposure and increased risk of respiratory infections.It is suggested that PM_2.5 exposure may weaken the innate defense of respiratory tract and make bacterial colonization easier,thus leading to the increase of respiratory tract infection.ObjectivesThe effects and potential mechanisms of short-term exposure to PM_2.5 on respiratory innate immune function were evaluated from the aspects of respiratory inflammatory response,innate defense protein level and microbial community structure,so as to provide new evidence for protecting public health.MethodsIn this study,healthy university volunteers from Xinxiang Medical College were recruited and selected according to the inclusion and exclusion criteria.Physical examination was conducted in winter（December 2020）and spring（April 2021）respectively.The pulmonary indicators including forced vital capacity（FVC）,forced expiratory volume in one second（FEV1）,peak expiratory flow（PEF）,minute ventilation（MV）and FVC/FEV1,the levels of inflammatory factors including interleukin-6（IL-6）,tumor necrosis factor-α（TNF-α）,IL-1β,interleukin-8（IL-8）,interferon-γ（IFN-γ）,interleukin-4（IL-4）and interleukin-17（IL-17）in nasal mucus and the innate immune protein lysozyme（LZM）and lactoferrin in nasal mucus were detected（LF）and secretory immunoglobulin A（SIg A）as well as innate immune proteins in sputum along with peroxidase（MPO）and matrix metalloproteinase 9（MMP-9）.Meanwhile,16Sr RNA sequencing was used to detect the abundance of microflora in some nasal mucus and sputum.Individual exposure(24-hour mean ambient PM_2.5concentration)was assessed based on the time of physical examination and PM_2.5concentration recorded at each follow-up visit.Taking PM_2.5 concentrations as the independent variable parameters and the research object of the innate immune effect index as the dependent variable parameters,controlling the influence of covariables,such as age,sex,body mass index（BMI）and season.A mixed linear effect model was introduced to evaluate the association between PM_2.5 concentrations and respiratory inflammation,innate immune protein levels and the relationship between the relative abundance of respiratory tract microorganism.Results53 healthy college students were included in the study,including 8 males（15.09%）and45 females（84.91%）,with an average age of（19.13±0.99）years and an average BMI of（22.61±4.02）kg/m~2.（1）The influence of PM_2.5 on lung function:PM_2.5 was significantly negatively correlated with lung function FEV1,FEV1/FVC and PEF.The concentration of PM_2.5（lag0）increased by 10μg/m~3,and the level of FEV1,FEV1/FVC and PEF decreased by0.43L（0.01～0.85）,0.13（0.05～0.21）and1.36L/s（0.36～2.35）.（2）The influence of PM_2.5 on the levels of respiratory inflammatory factors:PM_2.5was significantly positively correlated with the levels of respiratory inflammatory factors.Each 10μg/m~3 increase of PM_2.5（lag2）concentration was related to the increase of 100.64%（11.27%～190.01%）of IL-6 level in nasal mucus inflammation.Each 10μg/m~3 increase of PM_2.5（lag3）concentration can cause the levels of IL-6 TNF-αIL-17,IL-4 and IFN-γincreased by 21.25%（5.40%～37.10%）,26.23%（0.31%～52.13%）,22.41%（0.67%～44.15%）,27.42%（6.55%～48.29%）and 18.25%（4.63%～31.86%）respectively.（3）The influence of PM_2.5 on the level of respiratory tract innate immune protein:PM_2.5 was negatively correlated with innate immune protein levels.PM_2.5（lag0）concentration increased by 10μg/m~3,LF of nasal mucus decreased by 66.35%（3.29%～129.40%）.PM_2.5（lag0）concentration increased by 10μg/m~3,sputum MPO decreased by 5.56%（0.11%～11.00%）and MMP-9 decreased by 3.38%（0.00%～6.77%）.（4）Effects of PM_2.5 on respiratory microflora:There was a significant negative correlation between PM_2.5（lag3）concentration and microbial diversity index Chao1 in nasal mucus.Only Fusobacteria was negatively correlated with PM_2.5（lag3）concentration at phylum level.At family level,Neisseria and Pasteurelaceae in nasal mucus bacterial community were significantly positively correlated with PM_2.5（lag3）concentration.At genus level,it was found that the increase of PM_2.5（lag3）concentration could lead to the increase of Neisseria and Haemophilus.PM_2.5（lag3）concentration was negatively correlated with microbialαdiversity index Chao1 and Shannon in sputum.In addition,at phylum level,actinobacteria,Bacteroides and Fusobacteria were found to be significantly negatively correlated with PM_2.5（lag3）concentration.At family level,PM_2.5（lag3）concentration in sputum was significantly negatively correlated with Porphyromonadaceae,Neisseria and Pasteuraceae.At genus level,there was a significant negative correlation among 6 taxa in sputum.ConclusionsShort-term exposure to PM_2.5 can reduce lung function,increase the expression of respiratory inflammatory factors,decrease the expression of innate immune proteins,and reduce the bacterial diversity of respiratory tract in healthy college students.