t5 American beech Pollen

Nature

American Beech (Fagus grandifolia) is a medium-sized tree, ranging up to 25 meters in height. It is a shade-tolerant, slow-growing tree with a life span of around 200 years. The tree possesses a broad crown with widely spreading roots. The bark of the tree is thin, smooth, and bluish-grey. The leaves are elliptical, finely serrated, 6 to 14 centimeters long in size, dark bluish-green on the upper surface, and lightly toned underneath. Male flowers are arranged in a spherical structure on hanging stalks, while female flowers are positioned at leaf axils in proximity to the shoot tip point. The pyramidal nuts are arranged in pairs in a spiky husk (outer shell). Beech flowering season starts from the middle of April until May in North America and Europe. The oil of the nuts is utilized for cooking and lighting purposes. Birds and mammals also consume the nuts from this tree. The beech tree wood is used for making flooring, furniture, handles, and carton boxes (1). Beech wood is predominantly utilized in railroad ties, timber, pulpwood, veneer, and charcoal production (2). Creosote made from beech wood is also used for medicinal purposes like disinfectant, laxative, and cough treatment (3). 

Habitat

American beech can tolerate a wide variety of climatic conditions (2). Beech thrives with an average yearly temperature ranging between 4°- 21°C for growth. It usually prefers regions with annual precipitation between 760 and 1270 mm. However, its spread can also be observed in areas below 760 mm of rainfall, such as Michigan (580 mm) and Canada (640 mm). Beech can be found at varied altitudes depending on the local soil and climatic conditions (4). It is also capable of sustaining in areas with low sunlight (1). Deep, moist, rich, well-drained, loamy textured soil with high humus content (2) and a pH of 4.1 to 6.0 (4) is preferable for the growth of beech trees. 

Taxonomy

American beech (F. grandifolia) belongs to the family Fagaceae and genus Fagus. This genus is composed of 10 species of beech, of which American Beech is the one that originated from North America. As per a study, European beech (F. sylvatica), which is native to Europe, is reported as another species belonging to this genus (1). 

Tissue

Beech tree produces ellipsoidal shaped pollen grains of size 29 to 44 µm (major axis) and 29 to 39 µm (minor axis). Their surface is usually rough, grainy with verrulose-scabrate (wart-like) processes. The pollen grains are tricolporate (with three pores), however, two- pored or four-pored grain may occasionally be found. The grains have elliptical pores of a maximum length of 10 µm, split by a furrow and enclosed within a thick ring-like structure (1). No beech pollen allergens have been identified to date (6). 

Exposure to tree pollens such as beech may induce reactions like allergic rhinitis and asthma among allergic individuals. The symptoms of allergic rhinitis included sneezing, watery rhinorrhea, nasal congestion, and itchy tongue palate. These allergic rhinitis-mediated complications can further result in sleep deprivation, learning disability, diminished quality of life, and cognitive impairment in allergic patients (8).

Allergic rhinitis

A study was conducted in the US to know the prevalence of allergen sensitivity towards various aeroallergens in patients with allergic rhinitis. In this study, a skin prick test (SPT) was performed with 48 airborne allergens in 100 patients with allergic rhinitis. All (n = 100) patients showed positive SPT to single or multiple aeroallergens. Among these, a piece of graphical information represented positive SPT reactivity to beech tree and leaf antigen in around 16% - 17% of the patients (8). 

Asthma

A comparative aeroallergen study was conducted on 421 patients with asthma or allergic rhinitis in Busan, Korea. The results showed a 12.9% sensitization rate to beech pollen in children of age group ≤ 12 years and 12.7% in adults of age group 31-64 years (7).

In another study conducted on woodworkers from a furniture factory, the results revealed bronchial hyperresponsiveness and sore throat in the workers due to exposure to oak and beech wood dust (15).

Contact Dermatitis

Occupational contact allergy from beech wood has been reported in a non-atopic carpenter aged 49-years after exposure to beech wood dust. The patient presented acute oedematous dermatitis symptoms on his exposed skin parts like eyelids, neck, and upper chest area. The patients also tested positive for multiple patch tests for beech dust (14).

Allergenic molecules

No American beech allergens have been identified to date. One allergen Fag s 1, from European beech (Fagus sylvatica) species belonging to the same genus Fagus, has been identified and listed by the IUIS database (6). A study reported Fag s 1 showing 69% of sequence identity with Bet v 1, a major birch allergen (17). 

Biomarkers of severity

Beech pollen allergen is reported to have structural similarity with Bet v 1 allergen and its homologs. Due to this similarity, IgE-reactivity to Bet v 1 is utilized for detecting sensitization to beech pollen among allergic patients. Thus, Bet v 1 is considered as the marker allergen and principal source for diagnosing sensitization to pollen from species of the beech family (18).

Cross-reactivity

A high degree of cross-reactivity between species of the family Fagaceae has been demonstrated (19). Studies have shown IgE cross-reactivity between beech pollen with tree pollens from the same order Fagales such as birch (12) and oak (19).

Additionally, the study revealed a significant positive correlation between beech and plane tree pollen (p<0.01) (19). According to another study, beech and oak pollen allergy might be manifested by cross-sensitization to grass pollen allergens (12).