# Pollen-Food Allergy Syndrome: Allergens, Clinical Insights, Diagnostic and Therapeutic Challenges
## 6 Protein Families Involved in PFAS
### Pathogenesis-Related Protein Group 10 (PR-10 Proteins)  
The PR-10 protein family, with Bet v 1 (17.5 kDa) from birch pollen as its prototype, is one of the most extensively studied allergen families implicated in PFAS [48]. These proteins are part of the pathogenesis-related protein class 10 family, which plays a defensive role in plants, helping them respond to environmental stressors such as pathogens, pests, and physical damage [123; 124; 125]. In humans, however, these proteins act as allergens, triggering immune responses in individuals sensitized to pollen.  
The prevalence of birch pollen allergy varies significantly across regions, particularly in Europe, where birch trees are widespread and a major source of seasonal pollen exposure [47]. Sensitization to birch pollen affects approximately 8% to 16% of the general population in Europe, with higher rates reported in countries with dense birch forests, such as Scandinavia and parts of Central Europe [126], but also China [127]. The prevalence of PR-10-mediated PFAS is particularly high in regions where birch pollen allergy is common, where it may affect more than 75% of birch-allergic patients [57; 127], as this geographic correlation reflects the widespread sensitization to Bet v 1, which primes the immune system to recognize structurally similar proteins in fruits, vegetables, and nuts [43; 57].  
PR-10 proteins are characterized by their small molecular size (17-18 kDa) and structural features, including a hydrophobic cavity that binds small ligands [128; 129]. This structural similarity across different plant species accounts for the high degree of cross-reactivity between PR-10 proteins in pollen and homologous proteins in plant-based foods. For instance, individuals allergic to birch pollen (Bet v 1) often experience symptoms after consuming raw apples (Mal d 1), apricots (Pru a 1f), cherries (Pru av 1), peaches (Pru p 1), celery (Api g 1), soy (Gly m 4), peanuts (Ara h 8), hazelnuts (Cor a 1), chestnuts (Cas s 1), or tomatoes (Sola 1 4), because of shared epitopes recognized by IgE antibodies [57; 100].  
One defining feature of PR-10 proteins is their heat- and digestion-labile nature. These proteins denature rapidly upon exposure to heat or enzymatic digestion in the gastrointestinal tract, which largely limits their allergenic effects to the oropharyngeal region [73]. As a result, PR-10-mediated PFAS typically manifests with mild oral symptoms, such as itching,  
Figure 3: Global distribution of key plants associated with PFAS, highlighting the most relevant species and their geographical ranges [121; 122]. Created with ChartMap.net.  
tingling, and swelling of the lips, tongue, throat, and palate. These localized reactions are often transient, resolving within minutes to half an hour after food ingestion [130]. Additionally, the ability of PR-10 proteins explains why cooked or processed forms of implicated foods are generally well-tolerated by most patients [129]. However, despite their mild nature, PR-10-mediated symptoms can significantly impact quality of life, especially in individuals with extensive cross-reactivities who must avoid a variety of fresh plant-based foods.