Birch pollen can cause massive problems for allergy sufferers
Photo: Karl-Josef Hildenbrand / picture alliance / dpa
Almost every or every seventh German suffers from hay fever at some point in his life.
And people who live in cities with more air pollution may be particularly affected.
At least that's what a Polish study in the specialist magazine »PLoS One« suggests.
According to this, pollen from urban trees could be more allergenic than that from trees in regions with clean air.
However, independent experts criticize the work.
What seems clear is that the allergy burden caused by pollen has increased significantly in recent decades.
Man-made climate change changes the growth periods of plants, pollen fly earlier and over a longer period of time.
Added to this are the burdens of introduced species such as ragweed.
In addition, heat and drought stress plants.
And that could ensure that on the one hand they produce significantly more pollen, but on the other hand that they release more allergy-causing proteins as a defense.
It is unclear, however, whether urban pollen is more aggressive than rural pollen - a question that a Polish research team has now addressed.
The group led by Monika Ziemianin from the Polish Academy of Sciences in Kraków wanted to determine how different levels of air pollution affect the condition of birch trees and the chemical composition of the pollen.
In the silver birch, which produces the most allergenic pollen among the trees in large parts of Europe, the protein Bet v 1 is the main allergen.
For their study, the team examined at least three trees in seven locations in south-eastern Poland, including smaller towns and the urban area of Kraków, as well as a forest as a reference area.
Looking at the photosynthetic efficiency and pigment composition of the leaves, the team found little difference between urban and rural birches.
According to the authors, however, analysis of the pollen using Raman spectroscopy revealed measurable deviations in the folding structure of the protein Bet v 1. In addition, pollen from trees in more polluted locations had a higher Bet v 1 concentration.
The team writes that this could increase allergenicity.
Green space planning ideas
For Jeroen Buters from the Center for Allergy & Environment (ZAUM) at the TUM-Helmholtz Zentrum München, however, the study contains weaknesses: Specifically, the toxicologist names a questionable collection method with too few samples that were taken at an undisclosed time.
Buters has long studied pollen allergies, and in a 2010 study showed that the release of Bet v 1 from the same amount of pollen can vary by more than 10-fold between different days within a year.
During the maturation process, the amount of Bet v 1 increases dramatically every day.
It is therefore extremely important when the pollen samples were taken, says Buters: »Taking three trees per location as a sample is not enough.
We collected from over 30 trees and it was still difficult despite the large number of samples.«
Stefanie Gilles, Head of the Department of Environmental Immunology at the University of Augsburg, mentions another problem: According to the expert, the conclusion that the differences in the pollen actually lead to an increased immune reaction in allergy sufferers is not permissible.
According to Gilles, no corresponding tests were carried out on patients with the pollen samples.
Experiments in the laboratory, on mice or on birch pollen allergy sufferers would be essential to support such a conclusion.
Nevertheless, the finding that the allergenicity of birch pollen could be increased by traffic emissions should be taken seriously - after all, birch trees are still very common in cities: "When planning new green spaces in the future, care could be taken to avoid the use of highly allergenic plants such as Planting hazel, alder or birch in places where air pollution is high,” says Gilles.