Epidemiologic studies reveal a dramatic increase in allergies in the last decades. Air pollution is considered to be one of the factors responsible for this augmentation.
Air pollution causes plants to express stress-induced factors with increased allergenicity. Extracts from birch pollen collected in urban areas had higher chemotactic activity on human neutrophils.
The increase in proinflammatory substances such as pollen-associated lipid mediators might contribute to the described urban-rural gradient of allergy prevalence.
Impact of Urbanization on the Proteome of Birch Pollen and Its Chemotactic Activity on Human Granulocytes. Bryce M, Drews O, Schenk MF, Menzel A, Estrella N, Weichenmeier I, Smulders MJ, Buters J, Ring J, Görg A, Behrendt H, Traidl-Hoffmann C. Int Arch Allergy Immunol. 2009 Aug 6;151(1):46-55.