A field experiment conducted by scientists from the University of Milano-Bicocca has demonstrated that high levels of car pollution causes Ragweed pollen (Ambrosia artemisiifolia L.) to be more allergenic.
This has the inconvenient and worrisome effect of causing more people to develop allergies to the pollen in their environment. Interestingly, the difference does not lie in the percentage of pollen grains distributed by plants along high-traffic roads compared to plants found in lower-traffic areas. Rather, the difference was found in the allergenicity of the pollen grains themselves, where the pollen collected from the plants in higher-traffic areas contained more allergens than their low-traffic counterparts.
Now, if you or someone in your household suffers from seasonal allergies, you are surely aware of pollen’s role in allergic diseases. Pollen, a notable source of allergens, is one of the most important contributing factors in the increased prevalence of allergies amongst the general population. When your body reacts to pollen, your immune system cells release histamines, which are responsible for inflammatory responses. This is why people who have allergies take antihistamines, which suppress the unnecessary inflammatory response triggered by harmless pollen grains.
Pollutants are already known to contribute to an increase in pollen allergies, also called pollinosis, because pollution can damage the mucous membranes in an individual’s airway passages, thus making it easier for allergens to penetrate the cells of the immune system.
In laboratory settings, however, pollutants have also been shown to affect plant growth and reproduction. They can interact with pollen grains by affecting their cell wall structure, allowing more allergens or sub-pollen particles to be released into the environment.
In some cases, pollutants bind to allergen-carrying particles forming complexes that enhance the allergic reaction in individuals. Finally, some plants express new allergenic proteins or modify the amount of allergens produced when they interact with pollutants. This study is one of the first studies to clearly demonstrate a link between the allergenicity of plants and pollution levels in a natural environment.
The scientists conducted this study, published in the European Journal of Allergy and Clinical Immunology, in the Po River Plains of Italy. In order to determine the level of pollen emission of the Ragweed plants, Alessandra Ghiani and her team collected mature pollen grains from the Ragweed plants that grow along popular main roads as well as in more remote areas. After collection, the scientists calculated the percentage of sub-pollen particle-releasing grains using microscopes and image analysis. They also used immunochemistry and liquid chromatography-mass spectrometry (LC-MS/MS) to quantify the allergenicity and the allergen pattern of various pollen samples.
Ghiani and her team found that Ragweed plants growing along high traffic roads caused higher immunoglobulin E reactivity, meaning that the allergens in Ragweed plants found in high-traffic areas caused a more pronounced immune system reaction, where histamines were released in larger quantities from immune system cells, causing a stronger inflammatory response.
Interestingly, Ragweed plants separated from streets by areas of high, dense vegetation were much less allergenic than those that were in direct contact with motor vehicle-related pollutants. This is likely caused by the separating vegetation’s ability to remove pollutants from the environment. This highlights the importance of distance between Ragweed plants and traffic areas in controlling allergy sensitivities among the public.
As mentioned above, there was no difference between the number of sub-pollen particles-releasing grains found in the environment across locations. Therefore, the group concludes that the weakening of the cell wall due to pollutants is species-specific and does not take place in this particular Ragweed plant.
The team of scientists acknowledged the study’s limitations, as minor changes in climate between sampling sites might also play a role in the different allergenicity encountered at various sites. They feel confident, however, that their results demonstrate a clear relationship between pollen allergenicity and traffic-related pollutants, where traffic pollution makes pollen more allergenic, directly contributing to an increase in sensitization rates.
Ghiani, A., Aina, R., Asero, R., Bellotto, E., & Citterio, S. (2012). Ragweed pollen collected along high-traffic roads shows a higher allergenicity than pollen sampled in vegetated areas Allergy, 67 (7), 887-894 DOI: 10.1111/j.1398-9995.2012.02846.x