Page - 56 - in Biodiversity and Health in the Face of Climate Change

56 symptoms are manifested, it is crucial to define the threshold of airborne concentra- tions of pollen that provoke these symptoms. However, it is well known that defin- ing such thresholds involves highly demanding and complicated investigations, with values varying between sites, countries, geoclimatic regions, different years and per pollen type (de Weger et  al. 2013). 3.4 Adjuvant Factors from  Pollen and  Impact of  Environmental Factors When we are exposed to pollen, it is not only the allergenic proteins that we inhale that affect us, but also our mucosa and/or skin are exposed to biochemically com- plex particles. Indeed, the allergenicity of pollen is not only the result of the allergen but also of adjuvant factors from pollen, such as lipids and pollen-derived adenosine (Dittlein et  al. 2016; Gilles-Stein et  al. 2016). Thus, exposure to allergens is neces- sary but not sufficient for the development of allergy (Gilles et  al. 2009). By analys- ing the pollen’s metabolome, Gilles et  al. (2011) found that pollens release a wide array of different bioactive substances such as sugars, lipids, secondary metabolites and hormones. Notably, these bioactive mediators bind to receptors on human immune cells, which could promote allergic sensitisation to pollen-derived proteins or boost already manifested allergic immune responses. These substances, apart from the allergen itself, could be responsible for the potency of the allergenicity of pollen. Furthermore, these adjuvant mediators are influenced by environmental fac- tors such as ozone (Beck et  al. 2013). Only recently has part of the pollen microbi- ome been discovered (Obersteiner et  al. 2016). This microbiome of pollen is not only species-specific, but also influenced by environmental factors (Obersteiner et  al. 2016). 3.5 New Pollen Allergies: The  Case of  Ragweed The European and Mediterranean Plant Protection Organization has reported the species Ambrosia artemisiifolia L. (common ragweed; Fig.  3.2) as an invasive and alien plant (Brunel et  al. 2010). Apart from being a harmful weed, its pollen is highly allergenic. As ragweed has become naturalised in Europe, it is now quite common in regional flora in many areas across the continent (Smith et  al. 2013). This expansion in European flora is expected to be reflected in human health by increasing sensitisation rates in allergic individuals (Burbach et  al. 2009). These rates have already been reported as extremely high, often reaching 80% (Table  3.1). The most commonly implicated allergen is Amb a 1. There is already evidence of increasing long-term trends in Ambrosia-specific IgE antibodies from 20% in the A. Damialis et  al.