Hay fever may sound like a pastoral malady, but city-dwellers can also be hit hard by pollen allergies. Now researchers have revealed a possible factor, finding that birch trees growing in heavily polluted urban areas have higher levels of a key allergen in their pollen.
Birch tree pollen is one of the most potent allergens. About 25% of people with hay fever affected by allergy to it, according to Allergy UK.
Research has found that urbanisation and air pollution may make the situation worse by increasing the concentration of a key allergen within birch tree pollen, and affecting the structures adopted by such proteins – a finding the team suggests may make them more potent.
“The results may explain the failures in the treatment of people with pollen allergy living in polluted areas, which should be considered by physicians, especially during the birch pollen seasons,” the authors report.
“Moreover, when greenery in the cities is planned, allergenic trees should not be planted, because, despite the fact that they can physiologically adapt to the local environment, they produce more stress proteins of a higher potential allergenicity.”
Writing in the journal Plos One, researchers in Poland reveal how they collected pollen samples from birch trees growing in seven locations in the Małopolska region of southern Poland – including a forested area, low-traffic streets and three locations in the city of Kraków – and measured the concentration of a key allergen called Bet v1. The male catkins were collected before the flowers fully opened in early spring.
The researchers explored the levels of various different types of air pollution between 2017 and 2019 at the seven sites, including nitrogen oxides and tiny particles known as PM2.5 and PM10, using an official database.
The team write that the average Bet v1 concentration measured in pollen samples collected at the Kraków sites, where the levels of nitrogen oxides were found to be particularly high, was significantly higher than at the less polluted sites. Samples from one Kraków site had a mean concentration of about 3,000ng of Bet v1 per 10mg of pollen, compared with around 750ng per 10mg in samples from the forested area.
The team say the findings chime with their previous work, which looked at the relationship between PM10 levels and Bet v1 concentration in 20 study sites, which also revealed that more polluted areas had higher levels of the allergen.
The latest study further suggests that the structures formed by the Bet v1 protein collected in areas with greater air pollution are different to those from less polluted areas. The authors suggest such differences may increase the allergenicity of Bet v1, but the study does not include experiments to investigate this.
Margaret Kelman, the acting head of clinical services at Allergy UK, which was not involved in the work, said the findings were in keeping with previous research, noting that studies have suggested warming temperatures globally and an increase in air pollution potentially contribute to more intense pollen seasons and an increase in circulating airborne pollen particles, making hay fever symptoms worse.
She also said urbanisation and air pollution increase the amount of carbon dioxide in the atmosphere, which has a negative effect on the immune system’s ability to fight infection and can contribute to worsening symptoms of allergy.
“This research aligns with previous studies that have found that levels of allergic rhinitis are higher in urban populations than in less polluted areas and that there is a correlation between carbon emissions and an increase in airborne pollen, and increased allergenicity of the pollen itself.”
