Exposure to air pollutants and birch pollen - pulmonary effects in allergic asthma

Abstract

Allergies are on the rise and air pollution seems to be an important contributing factor. Exposure to birch pollen is a key trigger for both allergies and asthma, but whether there are synergistic effects between air pollutants and pollen is not fully clear. Both exposures harm the airway barrier in small airways and thereby contribute to the onset and progression of asthma. The aim of this thesis was to characterize exposure to air pollutants in and outside the pollen season and to explore the effects of exposure on the composition of phospholipids in the lining fluid of small airways in allergic asthma. Personal exposure measurements of air pollutants followed by a clinical examination, were conducted during two consecutive pollen seasons and once outside the pollen season in subjects with allergic asthma and allergy to birch and in healthy controls. Liquid particles formed in the small airways and sampled in breath (PEx) were analyzed with liquid chromatography-mass spectrometry (LC-MSMS). Data were analyzed with mixed models and multivariate methods. The results showed that around 50-70% of the variation in personal exposure levels was explained by background levels of the corresponding pollutant. Exposure to PM2.5 during the pollen season was associated with increased rhinitis/eye irritation and medication use, and exposure to O3 with dry cough. Seventy-eight different lipid species belonging to seven different lipid classes were identified in PEx. The phospholipid composition of PEx was altered in subjects with asthma and amplified in the pollen seasons. The profile of phospholipids was also associated with the level of asthma control, where there was a positive association between the level of control and linolenic acid and a negative association with arachidonic acid (i.e. the lower- control the higher linoleic acid). The response to pollutants differed significantly between subjects with asthma and healthy control in the distribution of eight phospholipid species. However, when analyzing the groups separately, a large number of phospholipids (n=57) were significantly associated with personal exposure to ozone, PM10, or NOx in healthy subjects, both in and outside the pollen seasons, whereas only four lipids showed significant associations in subjects with asthma. In conclusion, the results showed that stationary measurements of air pollutants only are moderately associated with personal measurements. Exposure to both pollen and air pollutants affects the phospholipid profile in the lining fluid in small airways, also at low concentrations. The effects of exposure seem to differ in subjects with asthma compared to healthy controls.