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Background: Experimental challenge studies have shown that pollen can have early and delayed effects on the lungs and airways. Here, we qualitatively and quantitatively synthesize the evidence of outdoor pollen exposure on various lung function and airway inflammation markers in community-based studies., Methods: Four online databases were searched: Medline, Web of Science, CINAHL and Google Scholar. The search strategy included terms relating to both exposure and outcomes. Inclusion criteria were human-based studies published in English that were representative of the community. Additionally, we only considered cross-sectional or short-term longitudinal studies which investigated pollen exposure by levels or season. Study quality assessment was performed using the Newcastle-Ottawa scale. Meta-analysis was conducted using random-effects models., Results: We included 27 of 6551 studies identified from the search. Qualitative synthesis indicated associations between pollen exposure and predominantly type-2 inflammation in both the upper and lower airways, but little evidence for lung function changes. People with ever asthma and/or seasonal allergic rhinitis (SAR) were at higher risk of such airway inflammation. Meta-analysis confirmed a positive relationship between pollen season, eosinophilia and eosinophil cationic protein (ECP) in people with ever SAR but the results between studies were highly variable. Heterogeneity was reduced after further subgrouping by age, and the forest plots indicated that eosinophilic airway inflammation to outdoor pollen exposure increased with age., Conclusion: Among people with ever asthma and ever SAR, exposure to increased ambient pollen triggers type-2 upper and lower airway inflammation rather than a non-specific or innate inflammation. These findings can lead to the formulation of specific pollen immunotherapy for susceptible individuals. Future research should be directed towards investigating lagged associations and effect modifications using larger and more generalized populations., Systematic Review Registration: CRD42020146981 (PROSPERO)., (© 2021 John Wiley & Sons Ltd.)

Background: The association between grass pollen exposure and early markers of asthma exacerbations such as lung function changes and increase in airway inflammation is limited. We investigated the associations between short‐term grass pollen exposure and lung function and airway inflammation in a community‐based sample, and whether any such associations were modified by current asthma, current hay fever, pollen sensitization, age, and other environmental factors. Methods: Cross‐sectional and short‐term analyses of data from the Melbourne Atopy Cohort Study (MACS) participants (n = 936). Lung function was assessed using spirometry. Airway inflammation was assessed by fractional exhaled nitric oxide (FeNO) and exhaled breath condensate pH and nitrogen oxides (NOx). Daily pollen counts were collected using a volumetric spore trap. The associations were examined by linear regression. Results: Higher ambient levels of grass pollen 2 days before (lag 2) were associated with lower mid‐forced expiratory flow (FEF25%‐75%) and FEV1/FVC ratio (Coef. [95% CI] = −119 [−226, −11] mL/s and −1.0 [−3.0, −0.03] %, respectively) and also 3 days before (lag 3). Increased levels of grass pollen a day before (lag 1) were associated with increased FeNO (4.35 [−0.1, 8.7] ppb) and also at lag 2. Adverse associations between pollen and multiple outcomes were greater in adults with current asthma, hay fever, and pollen sensitization. Conclusion: Grass pollen exposure was associated with eosinophilic airway inflammation 1‐2 days after exposure and airway obstruction 2‐3 days after exposure. Adults and individuals with asthma, hay fever, and pollen sensitization may be at higher risk. [ABSTRACT FROM AUTHOR]

Background Experimental challenge studies have shown that pollen can affect the lungs and airways. Here, we systematically reviewed community-based studies investigating outdoor pollen exposure, lung function and/or airway inflammation. Methods Four online databases were searched. The search strategy included terms relating to both exposure and outcomes. Inclusion criteria were studies published in English that were representative of the community. We only considered cross-sectional or short-term longitudinal studies which investigated pollen exposure by levels or season. Study quality assessment was performed using the Newcastle-Ottawa scale. Meta-analysis was conducted using random-effects models. Results We included 27 of 6,551 studies identified from the search. Qualitative synthesis indicated associations between pollen exposure and predominantly type-2 inflammation in both the upper and lower airways, but little evidence for lung function changes. People with ever asthma and/or seasonal allergic rhinitis (SAR) were at higher risk of such airway inflammation. Meta-analysis confirmed a positive relationship between pollen season and eosinophilic airway inflammation in people with ever SAR but the results between studies were highly variable. Heterogeneity was reduced after further subgrouping by age and the forest plots indicated that eosinophilic airway inflammation to outdoor pollen exposure increased with age. Conclusion Among people with ever asthma and ever SAR, exposure to increased ambient pollen triggers type-2 airway inflammation rather than a non-specific or innate inflammation. Key messages This review indicates pollen exposure influences predominantly type-2 airway inflammation, but little evidence on lung function. [ABSTRACT FROM AUTHOR]