Different urban environments shape the allergenicity and immunotoxicity of birch pollen

Interactions with air pollutants can modify pollen properties, thereby altering their allergenicity and even the severity of pollen-induced symptoms. This study aimed to examine whether birch pollen collected from locations with varying degrees of urbanization and traffic exposure differs in allergen content and immunotoxic properties. To our knowledge, this is the first study to integrate in situ birch pollen sampling across contrasting urban environments with morphological, chemical, and immunotoxic profiling in two complementary human cell models. Birch pollen samples were collected from four locations in Kuopio, Finland, including a low-traffic residential area, an urban park, and two sites adjacent to major roads and a highway. Elemental composition was analyzed using scanning electron microscopy. Pollen viability and allergen content were assessed by trypan blue staining and ELISA. Immunotoxic properties of pollen, including viability, metabolic activity, oxidative stress, and cytokine production, were assessed using two cellular models: a co-culture of human alveolar epithelium and macrophages, and peripheral blood mononuclear cells (PBMCs). Pollen from high-traffic locations contained more metallic elements. Allergen (Bet v 1) concentrations were 2.6-fold higher in pollen from the highway site compared to the pollen collected from the residential area. Pollen viability followed a similar pattern, lowest near the highway and highest in the residential area. Pollen from the city center induced the highest cytokine (i.e., TNF-α, GM-CSF, and MIP-1β) release in airway cell model. While cell viability and metabolic activity remained largely unaffected, oxidative stress responses varied, with the highest levels observed in pollen from highway-adjacent trees. These findings suggest that pollen collected near high-traffic areas may have increased potential to trigger allergic inflammation and respiratory distress. The elemental composition of pollen and the immune responses it induced varied across sampling sites, indicating the complexity by which environmental factors can influence pollen properties and potential health effects.